Light guide member and image display device

Abstract

To provide a light guide member that maintains a good positional relationship between multiple aligned light guide means, and that, when applied to an image display device, can provide the viewer with an image with excellent image quality and brightness. [Solution] An embodiment of the present invention provides a light guide member comprising: a first light guide means into which light is incident, guided, and emitted; and a second light guide means into which light emitted from the first light guide means is incident, guided, and emitted. The first light guide means and the second light guide means each include a diffraction grating; the first light guide means and the second light guide means are laminated with an intermediate layer in between; and the refractive index n3 of the intermediate layer is lower than the refractive index n1 of the first light guide means and the refractive index n2 of the second light guide means, respectively.

Description

Technical Field

[0001] The present invention relates to a light guide member and an image display device.

Background Art

[0002] In recent years, so-called AR (Augmented Reality) technology has attracted attention. AR is typically a technology that "virtually expands" the world in front of the viewer by overlaying virtual visual information on a real landscape. Along with the development of AR, development of wearable displays such as AR glasses and head mounted displays (HMD) used in AR has been progressing. A wearable display typically uses a light guide plate for guiding virtual visual information (typically, an image generated by an image generation device) into the viewer's field of view. Here, conventional wearable displays have a problem that the eye box (the range in which an image can be fully viewed even if the position of the eye shifts) is small. In order to solve such a problem, a technique using a plurality of aligned light guide plates has been proposed (Patent Document 1). However, in the technique of Patent Document 1, alignment of the light guide plates is complicated, and further, the image quality and brightness of the generated image visually recognized by a viewer may be insufficient.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] The present invention was made to solve the above-mentioned conventional problems, and its main objective is to provide a light guide member that maintains a good positional relationship between a plurality of aligned light guide means and can provide viewers with images of superior quality and brightness when applied to an image display device. [Means for solving the problem]

[0005] [1] An embodiment of the present invention provides a light guide member comprising: a first light guide means into which light is incident, guided, and emitted; and a second light guide means into which light emitted from the first light guide means is incident, guided, and emitted. The first light guide means and the second light guide means each include a diffraction grating; the first light guide means and the second light guide means are laminated with an intermediate layer in between; the refractive index n3 of the intermediate layer is lower than the refractive index n1 of the first light guide means and the refractive index n2 of the second light guide means, respectively. [2] In the above [1], the refractive index n1 of the first light guiding means, the refractive index n2 of the second light guiding means, and the refractive index n3 of the intermediate layer satisfy the following relationship. n3 / n1≦0.90 n3 / n2≦0.90 [3] In the above [1] or [2], the refractive index n3 of the intermediate layer is 1.30 or less. [4] In any of the above [1] to [3], the intermediate layer is a porous layer. [5] In any of the above [1] to [4], the diffraction grating is a reflective volume hologram. [6]According to another aspect of the present invention, an image display device is provided which can be worn by a viewer and comprises an image generating device and any of the light guiding members described in [1] to [5] above. In the image display device, light emitted from the image generating device is incident on the first light guiding means, and the second light guiding means emits light toward the viewer's pupil. [7] In the above [6], the image display device is AR glasses or a head-mounted display. [Effects of the Invention]

[0006] According to embodiments of the present invention, the positional relationship of a plurality of aligned light guide means is well maintained, and a light guide member can be realized that, when applied to an image display device, can provide the viewer with an image with excellent image quality and brightness. [Brief explanation of the drawing]

[0007] [Figure 1] This is a conceptual diagram of a light guide member according to one embodiment of the present invention. [Figure 2] This is a conceptual exploded perspective view of the light guide member in Figure 1, with the intermediate layer removed. [Figure 3] This is a conceptual diagram illustrating an example of a method for forming a hologram on a light-guiding means that can be used in a light-guiding member according to an embodiment of the present invention. [Figure 4] (a) is a conceptual diagram showing the cross-sectional light intensity distribution of light irradiated to form a hologram on a light guide means that can be used in a light guide member according to an embodiment of the present invention; (b) is a conceptual diagram showing the state of the photopolymer before and after irradiation with the light shown in (a). [Figure 5] This is a conceptual diagram of an image display device according to one embodiment of the present invention. [Figure 6] This is a schematic diagram showing a head-mounted display, which is an example of an image display device according to an embodiment of the present invention, as viewed from the front. [Figure 7] Figure 6 is a schematic diagram showing the head-mounted display being worn, viewed from above. [Modes for carrying out the invention]

[0008] The embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. For clarity, the drawings are schematic and conceptual, and the thickness, size, and relative proportions of the optical components shown in the drawings, as well as the thicknesses between components, may differ from those of actual components. Furthermore, there may be inaccuracies between drawings.

[0009] In this specification, for ease of understanding, the arrangement and configuration of each part may be described using the XYZ Cartesian coordinate system. In the XYZ Cartesian coordinate system, the direction in which the X-axis extends is referred to as the "X direction," the direction in which the Y-axis extends is referred to as the "Y direction," and the direction in which the Z-axis extends is referred to as the "Z direction." The direction in which the arrow indicating the X-axis points is denoted as the +X direction, and the direction opposite to the +X direction is referred to as the -X direction. The direction in which the arrow indicating the Y-axis points is referred to as the +Y direction, and the direction opposite to the +Y direction is referred to as the -Y direction. The direction in which the arrow indicating the Z-axis points is referred to as the +Z direction, and the direction opposite to the +Z direction is referred to as the -Z direction. In this specification, the +Z direction is referred to as "up," and the -Z direction is referred to as "down." However, these expressions regarding directions only describe the relative positions, orientations, and directions, and may not correspond to the relationships in actual use. Furthermore, these directions are unrelated to the direction of gravity. In this specification, "orthogonal" may include a deviation of ±10 degrees from 90 degrees. Similarly, "parallel" may include a deviation of ±10 degrees from 0 degrees.

[0010] A. Light guide member A-1. Overall configuration of the light guide member Figure 1 is a conceptual diagram of a light guide member according to one embodiment of the present invention; Figure 2 is a conceptual exploded perspective view of the light guide member of Figure 1 with the intermediate layer removed. The illustrated light guide member 100 comprises a first light guide means 10 and a second light guide means 20. The first light guide means 10 includes a diffraction grating 12. The diffraction grating 12 may be, for example, a reflective volume hologram. Hereinafter, the diffraction grating 12 may be simply referred to as the hologram 12 (the same applies to other diffraction gratings). The first light guide means 10 diffracts light L incident from above in the -Y direction by the hologram 12. The light L diffracted by the hologram 12 is guided in the -Y direction while undergoing total internal reflection at the upper surface 10a and lower surface 10b of the first light guide means 10, respectively. The light L is guided in the -Y direction and diffracted upward or downward by the hologram 12 and emitted. The second light guide means 20 typically includes a first hologram 22 and a second hologram 24. The first hologram 22 is typically positioned at a location corresponding to the hologram 12 of the first light guide means 10. Here, "corresponding location" means that at least a portion of the hologram 12 and the first hologram 22 overlap when the light guide member is viewed from above, preferably substantially all of them overlap. The second hologram 24 is positioned at a distance from the first hologram 22 in the light guide direction (+X direction) of the second light guide means 20. The second light guide means 20 diffracts the light L emitted from the first light guide means 10 and incident from above in the +X direction by the first hologram 22. The light L diffracted by the first hologram 22 is guided in the +X direction while undergoing total internal reflection at the upper surface 20a and lower surface 20b of the second light guide means 20, respectively. The light L guided in the +X direction is diffracted upward by the second hologram 22 and emitted.

[0011] The hologram 12 may be formed on the first light guide means itself (for example, as a hologram portion inside the first light guide means), or as a hologram layer on one of the main surfaces (upper surface 10a or lower surface 10b) of the first light guide means. Similarly, the first hologram 22 and the second hologram 24 may be formed on the second light guide means itself (for example, as a first hologram portion and a second hologram portion inside the second light guide means), or as a first hologram layer and a second hologram layer on one of the main surfaces (upper surface 20a or lower surface 20b) of the second light guide means.

[0012] The first light guide means 10 in the illustrated example is an elongated rectangle in the Y direction when viewed from above. The second light guide means 20 in the illustrated example is an elongated rectangle in the X direction when viewed from above, and its short side may correspond to the long side of the first light guide means 10. As described above, the first hologram 22 of the second light guide means 20 is provided in the second light guide means 20 at a position corresponding to the hologram 12. The second hologram 24 has a wider shape than the first hologram 22 in the light guiding direction (X direction) of the second light guide means 20. With such a configuration, the beam width of the light emitted from the first light guide means 10 along the Y direction (light guiding direction of the first light guide means) is greater than the beam width of the light incident on the first light guide means 10 along the Y direction; and the beam width of the light emitted from the second light guide means 20 along the X direction (light guiding direction of the second light guide means) is greater than the beam width of the light incident on the second light guide means 20 along the X direction. As shown in Figure 2, if the light L incident on the first light guide means 10 is schematically represented as a single beam, the light emitted from the first light guide means 10 is represented as three beams in the illustrated example, and the light emitted from the second light guide means 20 is represented as 3 × 3 = 9 beams in the illustrated example. In this way, with the above configuration, the incident light (virtual visual information, i.e., the image generated by the image generation device) can be magnified without magnifying the lens or other components on the image generation device side. As a result, when the light guide member is applied to a wearable display, the eye box can be significantly enlarged without increasing the size of the wearable display.

[0013] In one embodiment, the first light guiding means 10 and the second light guiding means 20 may each be configured to diffract (emit) a plurality of light beams having different wavelengths (or wavelength bands). When diffracting (emitting) three different types of light (for example, red, green and blue), the first light guiding means 10 and the second light guiding means 20 may each adopt a three-layer structure. More specifically, each of the three layers of the first light guiding means may be provided with a hologram on which interference fringes corresponding to the wavelengths (or wavelength bands) of red, green and blue are formed; each of the three layers of the second light guiding means may be provided with a first hologram and a second hologram on which interference fringes corresponding to the wavelengths (or wavelength bands) of red, green and blue are formed. With such a configuration, the three layers of the first light guiding means and the three layers of the second light guiding means can respectively guide and diffract (emit) red, green and blue light. Needless to say, the configuration for diffracting (emitting) a plurality of light beams having different wavelengths (or wavelength bands) is not limited to three layers, and may be two layers, or four or more layers (for example, four layers, five layers, six layers). For example, when diffracting (emitting) four different types of light (for example, red, green, blue and magenta), an additional layer including a hologram on which interference fringes corresponding to magenta are formed may be provided in the first light guiding means to form a four-layer structure; an additional layer including a first hologram and a second hologram on which interference fringes corresponding to magenta are formed may be further provided in the second light guiding means to form a four-layer structure.

[0014] In embodiments of the present invention, the first light guide means 10 and the second light guide means 20 are laminated via an intermediate layer 30. In one embodiment, the intermediate layer 30 may function as a bonding layer. In this case, the first light guide means 10, the intermediate layer 30, and the second light guide means 20 are directly laminated. In this specification, "direct lamination" means that two components (here, the first light guide means 10 and the second light guide means 20, and the intermediate layer 30) are laminated without an adhesive layer or tack layer in between. Here, "direct lamination" also includes the case where the first light guide means 10 and the second light guide means 20, and the intermediate layer 30 are laminated via an adhesion auxiliary layer (not shown). The adhesion auxiliary layer typically contains a silane coupling agent, and as will be described later, the formed adhesion auxiliary layer itself does not have an adhesive or tack function. Furthermore, as will also be described later, the thickness of the adhesion auxiliary layer is very small and may not be clearly recognized as a layer. Therefore, the above-described form via an adhesion auxiliary layer can also be included in "direct lamination". Furthermore, by providing an adhesion auxiliary layer, even greater strength can be achieved without impairing the light-guiding performance of the light guide member. In another embodiment, the first light guide means 10 and the second light guide means 20 may be laminated with an intermediate layer 30 via an adhesive layer (not shown). By laminating the first light guide means and the second light guide means via an intermediate layer, the following advantages can be obtained: (i) It is not necessary to align the first light guide means and the second light guide means and place them in the housing. In other words, complicated alignment can be omitted, which can improve the manufacturing efficiency of the light guide member. (ii) The first light guide means and the second light guide means can be precisely aligned. As a result, when the light guide member is applied to an image display device, an image with excellent image quality (for example, not blurry or difficult to see) can be provided to the viewer. (iii) Furthermore, since the positional relationship between the aligned first light guide means and the second light guide means is well maintained, the deterioration of image quality over time can be suppressed. (iv) Since the air layer can be eliminated, adverse effects on image quality caused by the air layer (e.g., image defects due to foreign matter, decrease in brightness due to condensation) can be prevented.

[0015] Further, the refractive index n3 of the intermediate layer 30 is lower than each of the refractive index n1 of the first light guiding means 10 and the refractive index n2 of the second light guiding means 20. With such a configuration, light propagation (light guiding) by total internal reflection in the first light guiding means 10 and the second light guiding means 20 can be improved while maintaining the aforementioned effect provided by the intermediate layer. Preferably, the refractive index n1 of the first light guiding means 10, the refractive index n2 of the second light guiding means 20, and the refractive index n3 of the intermediate layer 30 satisfy the following relationship. n3 / n1≦0.90 n3 / n2≦0.90 More preferably, n3 / n1 is 0.85 or less, and still more preferably 0.80 or less. The lower limit of n3 / n1 can be, for example, 0.70. More preferably, n3 / n2 is 0.85 or less, and still more preferably 0.80 or less. The lower limit of n3 / n2 can be, for example, 0.70. With such a configuration, the aforementioned effect can be more remarkable. The refractive index n3 of the intermediate layer 30 is preferably 1.30 or less. When n3 is within such a range, it can be easy to achieve the aforementioned n3 / n1 and n3 / n2.

[0016] Hereinafter, the constituent elements of the light guide member will be specifically described.

[0017] A-2. First Light Guiding Means and Second Light Guiding Means Hereinafter, the first light guiding means and the second light guiding means are collectively described as "light guiding means". When it is necessary to distinguish between the first light guiding means and the second light guiding means for description, "first" and "second" will be explicitly stated. The same applies to the holograms provided in the light guiding means, and reference numerals in the drawings will be explicitly stated when it is necessary to distinguish between them.

[0018] A-2-1. Overall Configuration of Light Guiding Means Typically, the light guide means is configured such that light incident on the light guide means propagates (guides light) within the light guide means using total internal reflection. The light guide means may be made of glass or resin. Examples of resins include thermoplastic resins and reactive resins (for example, non-ionizing radiation-curable resins such as ultraviolet, visible light, and infrared rays). Examples of thermoplastic resins include cellulose-based resins such as triacetylcellulose (TAC), COC resins and COP resins such as cyclic olefin copolymers and cycloolefin resins, acrylic resins such as polymethyl methacrylate (PMMA), styrene resins, polycarbonate (PC) resins, polyethylene terephthalate (PET) resins, resins mainly composed of one or more of the above, and transparent polyimide resins. Examples of reactive resins include non-ionizing radiation-curable resins (photopolymers) such as acrylic, epoxy, urethane, silicone, and enthiol-based resins. The light guide means may be constructed using, for example, "Bayfol® HX200" manufactured by Covestro.

[0019] The light guide means is typically light-transmitting. The transmittance of the light guide means for visible light is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more.

[0020] The refractive index of the light guide means is preferably 1.40 to 2.00, more preferably 1.45 to 1.90, and even more preferably 1.50 to 1.80. Within this refractive index range, good external light incidence, good external light emission, and good total internal reflection within the light guide means can be achieved.

[0021] The thickness of the light guide means is preferably 10 mm or less, more preferably 5 mm or less, and even more preferably 1 mm or less. If the thickness of the light guide means is within this range, the overall thickness of the light guide member can be reduced, and as a result, the light guide member can be suitably used in wearable displays such as AR glasses and HMDs. Practically, the lower limit of the thickness of the light guide means may be, for example, 100 μm, or for example, 200 μm.

[0022] A-2-2. Hologram As described above, the hologram 12 is provided at a predetermined position on the first light guide means 10; the first hologram 22 is provided at a position corresponding to the hologram 12 on the second light guide means 20; and the second hologram 24 is provided at a position separated from the first hologram 22 in the light guide direction of the second light guide means 20. Also as described above, the hologram 12 may be formed on the first light guide means itself (for example, as a hologram portion inside the first light guide means), or as a hologram layer on one main surface (upper surface 10a or lower surface 10b) of the first light guide means; the first hologram 22 and the second hologram 24 may be formed on the second light guide means itself (for example, as a first hologram portion and a second hologram portion inside the second light guide means), or as a first hologram layer and a second hologram layer on one main surface (upper surface 20a or lower surface 20b) of the second light guide means. Furthermore, any hologram can be a reflective volume hologram. A reflective volume hologram can selectively diffract light of a specific wavelength. More specifically, by using a reflective volume hologram in which interference fringes corresponding to a specific wavelength or wavelength band (e.g., red, green, or blue wavelengths or wavelength bands) are formed, light of that specific wavelength or wavelength band can be selectively diffracted.

[0023] Holograms can typically be composed of photopolymers. With such a configuration, interference fringes can be formed by exposure. Below, an example of a method for forming interference fringes will be described with reference to Figures 3 and 4. For ease of understanding, the case in which a hologram 12 is formed on the first light guide means 10 will be described. Furthermore, a method for forming interference fringes corresponding to green (wavelength 532 nm) will be described. In addition, although the case in which interference fringes (holograms) are formed on a photopolymer layer formed on a light guide member composed of a resin film will be described, if the light guide member itself is composed of a photopolymer, the interference fringes may be formed on the light guide member itself.

[0024] Figure 3 is a schematic perspective view illustrating an example of a method for forming a hologram on a light guide. As shown in Figure 3, a first laser beam B1, which is one of the laser beams branched from a laser beam with a peak wavelength of 532 nm, is irradiated from above onto the photopolymer layer 12' formed on the first light guide 10. Furthermore, a second laser beam B2, which is the other laser beam branched from the laser beam with a peak wavelength of 532 nm, is irradiated from below onto the photopolymer layer 12' through a lens Len. As a result, the photopolymer layer 12' is irradiated with light having an intensity distribution corresponding to the interference fringes fg generated by the interference of the first laser beam B1 and the second laser beam B2.

[0025] Figure 4(a) is a conceptual diagram showing the cross-sectional light intensity distribution of light irradiated to form a hologram on a light guide means that can be used in a light guide member according to an embodiment of the present invention; (b) is a conceptual diagram showing the state of the photopolymer before and after irradiation with the light shown in (a). The cross-sectional light intensity distribution fg1 in Figure 4(a) represents the cross-sectional light intensity distribution along the alignment direction fg0 of interference fringes fg arranged in the alignment direction fg0. The photopolymer layer 12' in Figure 4(b) represents the state of the photopolymer before irradiation with light having an intensity distribution corresponding to the interference fringes fg; the hologram 12 in Figure 4(b) represents the state of the photopolymer after irradiation with light having an intensity distribution corresponding to the interference fringes fg.

[0026] A photopolymer typically contains a binder 13 and multiple monomers 14. When light having an intensity distribution corresponding to interference fringes fg is irradiated, the positions of the multiple monomers 14 change according to the light intensity distribution of the interference fringes fg. In the example shown in Figure 4, the density of monomers 14 is high at locations where the light intensity of the interference fringes fg is high, and low at locations where the light intensity of the interference fringes fg is low. The refractive index is high at locations where the density of monomers 14 is high, and low at locations where the density of monomers 14 is low. When light having an intensity distribution corresponding to interference fringes fg is irradiated onto the photopolymer layer 12', a refractive index distribution corresponding to the light intensity distribution of the interference fringes fg is formed.

[0027] After forming a refractive index distribution corresponding to the light intensity distribution of the interference fringes fg at a predetermined position on the photopolymer layer 12' as described above, the monomer 14 is cured by irradiating the entire surface of the photopolymer layer 12' with ultraviolet light from, for example, a xenon light source. By curing the monomer 14, the refractive index distribution corresponding to the light intensity distribution of the interference fringes fg is fixed as a hologram 12. The refractive index distribution of the hologram 12 can cause the green light incident on the hologram 12 to be diffracted. For example, a hologram 12 that diffracts green light can be created using a semiconductor laser that emits laser light with a peak wavelength of 532 nm, with a laser light intensity of 20 mJ / cm². 2 This can be achieved by setting the angle θ between the optical axis B1c of the first laser beam B1 and the optical axis B2c of the second laser beam B2 to 130 degrees.

[0028] In this manner, a hologram 12 can be formed on the first light guide means 10. Similarly, a first hologram 22 and a second hologram 24 can be formed on the second light guide means 10.

[0029] By changing the type (wavelength) and irradiation conditions of the laser light, the shape (refractive index distribution) of the hologram can be controlled, and as a result, light of different wavelengths (colors) can be diffracted. For example, by using laser light with a peak wavelength in the range of 620 nm to 660 nm, a hologram 12 that diffracts red light can be formed; by using laser light with a peak wavelength in the range of 430 nm to 470 nm, a hologram 12 that diffracts blue light can be formed.

[0030] A-3. Middle Class The intermediate layer 30 can be any suitable configuration, as long as its refractive index n3 is lower than the refractive index n1 of the first light guide means 10 and the refractive index n2 of the second light guide means 20, respectively. The intermediate layer 30 is typically a porous layer having voids inside. The porosity of the intermediate layer is preferably 35 volume% or more, more preferably 38 volume% or more, and particularly preferably 40 volume% or more. If the porosity is within this range, an intermediate layer with a particularly low refractive index can be formed. The upper limit of the porosity of the intermediate layer is, for example, 90 volume% or less, and preferably 75 volume% or less. If the porosity is within this range, an intermediate layer with excellent strength can be formed. The porosity is a value calculated from the refractive index measured with an ellipsometer using the Lorentz-Lorenz formula.

[0031] The refractive index of the intermediate layer is preferably 1.30 or less as described above, but may also be, for example, 1.25 or less, 1.23 or less, 1.22 or less, 1.21 or less, 1.20 or less, or 1.19 or less. On the other hand, the refractive index of the intermediate layer may be, for example, 1.05 or more, 1.08 or more, or 1.10 or more. If the refractive index of the intermediate layer is within this range, adverse effects caused by the air layer can be eliminated, and excellent light guiding performance can be achieved in the first and second light guiding means. Furthermore, since the intermediate layer can be made very thin as described later, it can contribute to the thinning and weight reduction of the light guiding member (and consequently, AR glasses, HMD). Also, if the refractive index of the intermediate layer is within the above range, a predetermined mechanical strength can be ensured, and breakage can be suppressed. Unless otherwise specified, the refractive index refers to the refractive index measured at a wavelength of 550 nm or the refractive index converted to a 550 nm value from the measured value at other wavelengths and the refractive index wavelength dispersion. The refractive index can be measured, for example, as follows: After forming an intermediate layer on the light guide, it is cut to a size of 50 mm x 50 mm, and the resulting cut piece is bonded to the surface of a glass plate (thickness: 3 mm) via an adhesive layer. The center of the back surface of the glass plate (approximately 20 mm in diameter) is colored black with a marker to create a sample that does not reflect light from the back surface of the glass plate. The above sample is set in an ellipsometer (JAWoollam Japan: VASE), and the refractive index is measured under conditions of a wavelength of 550 nm and an incident angle of 50 to 80 degrees.

[0032] The total light transmittance of the intermediate layer is preferably 85% to 99%, more preferably 87% to 98%, and even more preferably 89% to 97%. When the total light transmittance of the intermediate layer is within this range, excellent transparency can be ensured while exhibiting the effects of the refractive index described above. As a result, the light guide member can be suitably used in wearable displays such as AR glasses and HMDs.

[0033] The haze of the intermediate layer is, for example, less than 5%, preferably less than 3%. On the other hand, the haze is, for example, 0.05% or more, preferably 0.1% or more. When the haze of the intermediate layer is within this range, excellent transparency can be ensured while exhibiting the effects of the refractive index described above. As a result, the light guide member can be suitably used in wearable displays such as AR glasses and HMDs. The haze can be measured, for example, as follows. An intermediate layer is formed on a 50mm x 50mm piece of glass, and the haze is measured using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute). The haze value is calculated using the following formula. Haze (%) = [Diffuse transmittance (%) / Total light transmittance (%)] × 100 (%)

[0034] The thickness of the intermediate layer is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, particularly preferably 2.5 μm or less, and especially preferably 2 μm or less. On the other hand, the thickness of the intermediate layer is preferably 300 nm or more, more preferably 400 nm or more, and even more preferably 500 nm or more. When the thickness of the intermediate layer is within this range, excellent transparency can be ensured while effectively suppressing light leakage. Furthermore, this can contribute to making the light guide member (and consequently AR glasses, HMD) thinner and lighter.

[0035] The surface roughness Rz of the intermediate layer is preferably 200 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less. This surface roughness ensures sufficient adhesion between the intermediate layer and the light guide means. Note that Rz refers to the maximum height according to JIS B 0601.

[0036] The intermediate layer can be any suitable configuration, as long as it has the desired properties described above. Examples of materials that can be used to constitute the intermediate layer include those described in International Publication No. 2004 / 113966, Japanese Patent Publication No. 2013-254183, and Japanese Patent Publication No. 2012-189802. Typical examples include silicon compounds. Examples of silicon compounds include silica-based compounds; hydrolyzable silanes, and their partial hydrolysates and dehydration condensates; silicon compounds containing silanol groups; and activated silica obtained by contacting silicates with acids or ion exchange resins. These materials may be used individually or in combination. The intermediate layer can be formed by coating or printing a solution or dispersion of such materials.

[0037] Details of the specific composition and formation method of the intermediate layer are described, for example, in International Publication No. 2019 / 151073. The description in said publication is incorporated herein by reference.

[0038] A-4. Adhesion support layer The adhesion auxiliary layer typically contains a silane coupling agent. Examples of silane coupling agents include acrylic silane coupling agents, amino silane coupling agents, epoxy silane coupling agents, and mercapto silane coupling agents. The silane coupling agent may be used alone or in combination of two or more types. In one embodiment, the silane coupling agent includes an acrylic silane coupling agent, and may also include a combination of an acrylic silane coupling agent with an amino silane coupling agent, an epoxy silane coupling agent, a mercapto silane coupling agent, or a combination thereof (another silane coupling agent). The acrylic silane coupling agent and the other silane coupling agent may each be used alone or in combination of two or more types. By providing an adhesion auxiliary layer containing a silane coupling agent, even greater strength can be achieved without impairing the light-guiding performance of the light-guiding member.

[0039] Acrylic silane coupling agents are typically silane coupling agents having a (meth)acrylic group in their skeleton. Examples of acrylic silane coupling agents include 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, methacryloxymethyltrimethoxysilane, methacryloxymethyltriethoxysilane, acryloxymethyltrimethoxysilane, acryloxymethyltriethoxysilane, and 3-methacryloxypropylmethyldimethoxysilane. Furthermore, many acrylic silane coupling agents are commercially available. Specific examples of commercially available products include KBM-502 and KBM-5103 manufactured by Shin-Etsu Chemical Co., Ltd. Preferably, 3-acryloxypropyltrimethoxysilane or 3-methacryloxypropylmethyldimethoxysilane are used.

[0040] Examples of amino-based silane coupling agents include γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-phenylaminopropyltrimethoxysilane, and 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine. Furthermore, many amino-based silane coupling agents are commercially available. Specific examples of commercially available products include KBM-903, KBE-9103, KBM-575, and KBM-6123 from Shin-Etsu Chemical Co., Ltd., and A-1102, A-1122, and A-1170 from Momentive Performance Materials Japan. Preferably, it is 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine.

[0041] Examples of epoxy silane coupling agents include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and γ-glycidoxypropylmethyldimethoxysilane. Furthermore, many epoxy silane coupling agents are commercially available. Specific examples of commercially available products include KBM-402 and KBM-403 manufactured by Shin-Etsu Chemical Co., Ltd. γ-glycidoxypropylmethyldimethoxysilane is preferred.

[0042] Examples of mercapto-silane coupling agents include γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, and γ-mercaptopropylmethyldiethoxysilane. Furthermore, many mercapto-silane coupling agents are commercially available. A specific example of a commercially available product is X-12-1056ES manufactured by Shin-Etsu Chemical Co., Ltd.

[0043] When using an acrylic silane coupling agent in combination with another silane coupling agent, the content ratio of the acrylic silane coupling agent to the other silane coupling agent is preferably 40 / 60 to 60 / 40, more preferably 45 / 55 to 55 / 45, even more preferably 47 / 53 to 53 / 47, and particularly preferably about 50 / 50, with the total amount of silane coupling agents being 100.

[0044] The thickness of the adhesion support layer is preferably as thin as possible, as long as it has the function of assisting adhesion between the light guide means and the intermediate layer. This is because it minimizes the adverse effect on light guide performance. Specifically, the thickness of the adhesion support layer is preferably 500 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, particularly preferably 10 nm or less, especially preferably 5 nm or less, and most preferably 4 nm or less. The thickness of the adhesion support layer may be, for example, 0.5 nm or more, or for example, 0.7 nm or more. The thickness of the adhesion support layer may be, for example, 0.8 nm to 3.5 nm, or for example, 0.9 nm to 3 nm. If the thickness of the adhesion support layer is very small (for example, 3 nm or less), it may not be clearly recognized as a layer.

[0045] The adhesion-enhancing layer can be formed by applying a solution of a silane coupling agent (silane compound) dissolved in a suitable solvent (e.g., water, isopropyl alcohol) to the surface of the light guide, and then drying the intermediate layer after lamination. As described above, the adhesion-enhancing layer itself does not have adhesive or tackiness after drying (formation), but it can assist and / or promote adhesion between the light guide and the intermediate layer as the coating film of the solution dries.

[0046] B. Image display device The light guide member described in Section A above can be suitably used in image display devices, and in particular suitably used in image display devices that can be worn by a viewer. Therefore, such image display devices can also be included in embodiments of the present invention. Image display devices that can be worn by a viewer are also called wearable displays. Typical examples of wearable displays include AR glasses and head-mounted displays (HMDs). Figure 5 is a conceptual diagram of an image display device according to one embodiment of the present invention. The illustrated image display device 200 comprises a light guide member 100 and an image generation device 120. In the image display device 200, light emitted from the image generation device 120 enters the first light guiding means 10 of the light guide member 100, and the second light guiding means 20 of the light guide member 100 emits light toward the viewer's pupil 52.

[0047] The configuration of the light guide member 100, as well as the incidence, propagation (light guidance), and emission of light in the light guide member 100, are as described in Section A above.

[0048] The image generation apparatus 120 typically includes an image forming apparatus 121 and a collimating optical system 122. The image forming apparatus 121 typically has a plurality of pixels arranged in a two-dimensional matrix. The collimating optical system 122 is typically configured to make the light emitted from each pixel of the image forming apparatus 121 into parallel light.

[0049] The image forming apparatus 121 typically includes a reflective spatial light modulator 130 and a light source 140 consisting of light-emitting diodes that emit white light. Specifically, the reflective spatial light modulator 130 includes a liquid crystal display (LCD) 131 consisting of an LCOS as a light bulb, and a polarizing beam splitter 132 that reflects a portion of the light from the light source 140 and guides it to the liquid crystal display 131, and also allows a portion of the light reflected by the liquid crystal display 131 to pass through and guide it to the collimating optical system 122. The liquid crystal display 131 has a plurality of pixels (for example, 320 × 240) arranged in a two-dimensional matrix. The polarizing beam splitter 132 has a structure and configuration well known in the industry, so a detailed explanation is omitted. Unpolarized light emitted from the light source 140 collides with the polarizing beam splitter 132. In the polarizing beam splitter 132, the P-polarized component passes through and is emitted out of the system. On the other hand, the S-polarized component is reflected by the polarizing beam splitter 132, incident on the liquid crystal display device 131, reflected inside the liquid crystal display device 131, and emitted from the liquid crystal display device 131. Here, of the light emitted from the liquid crystal display device 131, the light emitted from pixels displaying "white" contains a large amount of P-polarized component, and the light emitted from pixels displaying "black" contains a large amount of S-polarized component. Therefore, of the light emitted from the liquid crystal display device 131 and colliding with the polarizing beam splitter 132, the P-polarized component passes through the polarizing beam splitter 132 and is guided to the collimating optical system 122. On the other hand, the S-polarized component is reflected by the polarizing beam splitter 132 and returned to the light source 140. The collimating optical system 122 is composed of, for example, a convex lens, and an image forming apparatus 121 (essentially the liquid crystal display device 131) is positioned at the focal length of the collimating optical system 122 in order to generate parallel light. Each pixel of a liquid crystal display device consists of a red subpixel that emits red light, a green subpixel that emits green light, and a blue subpixel that emits blue light. A voltage can be applied to each subpixel to form an electric field. As a result, the liquid crystal is driven for each subpixel. By turning the liquid crystal drive on and off, red, green, and blue light are emitted from each subpixel according to the input signal. In this way, an image corresponding to the input signal can be formed.

[0050] Red, green, and blue light (represented by solid, dashed, and dotted lines, respectively) emitted from the image forming apparatus 121 and incident on the light guide member 100 (substantially the first light guide means 10) via the collimating optical system 122 are propagated (guided) within the light guide member 100 as described in section A above, and emitted from the second light guide means 20 toward the viewer's pupil 52. In this way, an image corresponding to the signal input to the liquid crystal display device is perceived by the viewer.

[0051] Next, a typical example of how an image display device can be used will be described. Figure 6 is a schematic diagram of a head-mounted display (HMD), an example of an image display device, as seen from the front; Figure 7 is a schematic diagram of the HMD in Figure 6 as seen from above. In Figure 7, only the image display device is shown, and the frame is omitted for clarity. The illustrated example HMD 300 comprises a glasses-type frame 310 worn by the viewer 50, and two image display devices 200, 200 provided to correspond to both eyes of the viewer 50.

[0052] The illustrated HMD300 further comprises a coupling member 320 that connects two image display devices 200, 200. The coupling member 320 is attached to the viewer-facing side of the central portion 310C of the frame 310, located between the two pupils 52, 52 of the viewer 50 (i.e., between the observer 50 and the frame 310), for example, using screws (not shown). The projected image of the coupling member 320 is contained within the projected image of the frame 310. That is, when the AR glasses are viewed from the front of the observer 50, the coupling member 320 is hidden by the frame 310 and is not visible. Specifically, the two image display devices 200, 200 have image generating devices 120, 120 attached to each end of the coupling member 320 in an adjustable manner. The image generating devices 120, 120 are located outside the pupils 52, 52 of the viewer 50. The image generating devices 120, 120 are attached to the connecting member 320 by any suitable means. For example, through holes (not shown) are provided at three locations at each end of the connecting member, and tapped holes (threaded parts: not shown) corresponding to the through holes are provided in the image generating devices 120, 120. Screws (not shown) are passed through each through hole and screwed into the holes provided in the image generating devices 120, 120. A spring is inserted between the screw and the hole. In this way, the mounting state of the image generating devices (the inclination of the image generating devices relative to the connecting member) can be adjusted by the tightening state of the screws. After mounting, the screws can be hidden with a cover (not shown) if necessary.

[0053] As described above, by attaching the image generation device to a connecting member rather than directly to the frame, the following advantages can be obtained. When the viewer 50 puts the frame 310 on their head, the temple portion 312 spreads outward. As a result, even if the frame 310 deforms, the displacement (change in position) of the image display devices 200, 200 can be suppressed, and preferably prevented. As a result, changes in the convergence angle of the left and right images can be effectively suppressed or prevented. Furthermore, since there is no need to increase the rigidity of the front part of the frame, the frame (and consequently the HMD) can be made lighter and less expensive. In addition, since the image display device is not directly attached to the frame, the viewer can freely select the design, color, etc. of the frame according to their preference. Therefore, the design options for the HMD can be expanded. These synergistic effects make it possible to realize an HMD with excellent fit and design.

[0054] The frame 310 has a front section 310B positioned in front of the observer 50, two temple sections 312 rotatably attached to both ends of the front section 310B via hinges 311, and temple tips (also called ear tips, ear pads) 313 attached to the ends of each temple section 312. The connecting member 320 is attached to the central section 310C of the front section 310B (corresponding to the bridge section in ordinary eyeglasses), which is located between the two pupils 52, 52 of the viewer 50, as described above. A nose pad 314 is attached to the side of the connecting member 320 facing the viewer 50. The frame 310 and the connecting member 320 are typically made of metal or plastic, respectively.

[0055] In the illustrated example HMD300, the image generation devices 120, 120, and the wiring (e.g., signal lines, power lines) 315 extending from them, pass through the inside of the temple section 312 and the modern section 313, and extend to the outside from the tip of the modern section 313, connecting to an external circuit (not shown). Furthermore, each of the image generation devices 120, 120 is equipped with a headphone section 316, and the headphone section wiring 317 extending from the image generation devices 120, 120, passes through the inside of the temple section 312 and the modern section 313, and extends from the tip of the modern section 313 to the headphone section 316. Specifically, the headphone section wiring 317 extends from the tip of the modern section 313, wrapping around the back of the auricle (earlobe) to the headphone section 316. With such a configuration, the headphone section 316 and / or the headphone section wiring 317 do not give the impression of being haphazardly arranged, resulting in an HMD with a superior appearance.

[0056] Furthermore, in the illustrated example HMD300, the imaging device 318 is mounted in the central portion 310C of the front portion 310B. Specifically, a through hole is provided in the central portion 310C, and a recess is provided in the portion of the coupling member 320 opposite the through hole, and the imaging device 318 is positioned within this recess. The imaging device 318 typically has a solid-state image sensor and a lens (neither of which are shown). Examples of solid-state image sensors include CCD and CMOS sensors. Light incident from the through hole in the central portion 310C is focused onto the solid-state image sensor by the lens. The signal from the solid-state image sensor is sent to one of the image generation devices 120 and then to an external circuit via wiring (not shown) extending from the imaging device 318. By connecting the imaging device to only one of the image generation devices, it is possible to make it difficult to see that the imaging device is incorporated into the HMD. As a result, an HMD with an excellent appearance can be made. The wiring passes between the connecting member 320 and the front section 310B and is connected to one of the image generation devices 120.

[0057] As shown in Figure 7, in the HMD300, the first light guiding means 10 and the second light guiding means 20 of the light guiding member included in the image display device 200 are stacked via a low refractive index intermediate layer 30. This provides the following advantages when worn by the viewer: (a) The viewer may be provided with images of excellent quality (e.g., not blurred or difficult to see). (b) The deterioration of image quality due to use (i.e., over time) may be suppressed. (c) For example, image defects due to foreign matter and a decrease in brightness due to condensation may be prevented. [Examples]

[0058] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" and "parts" in the examples are based on weight.

[0059] [Manufacturing Example 1] Preparation of coating solution for intermediate layer formation (1) Gelation of silicon compounds Mixture A was prepared by dissolving 0.95 g of methyltrimethoxysilane (MTMS), a precursor of silicon compounds, in 2.2 g of dimethyl sulfoxide (DMSO). To this mixture A, 0.5 g of 0.01 mol / L aqueous oxalic acid solution was added, and the mixture was stirred at room temperature for 30 minutes to hydrolyze the MTMS and produce mixture B containing tris(hydroxy)methylsilane. To 5.5 g of DMSO, 0.38 g of 28% by weight aqueous ammonia and 0.2 g of pure water were added. Then, the above mixture B was added, and the mixture was stirred at room temperature for 15 minutes to gel tris(hydroxy)methylsilane, obtaining mixture C containing a gel-like silicon compound. (2) Aging process The mixed solution C containing the gel-like silicon compound prepared as described above was incubated at 40°C for 20 hours to perform the maturation process. (3) Grinding Next, the gel-like silicon compound, which had been aged as described above, was crushed into granules of several mm to several cm in size using a spatula. Then, 40 g of isopropyl alcohol (IPA) was added to mixture C, and after light stirring, it was left to stand at room temperature for 6 hours to decantate the solvent and catalyst in the gel. By performing the same decantation treatment three times, the solvent was replaced to obtain mixture D. Next, the gel-like silicon compound in mixture D was subjected to pulverization (high-pressure medialess pulverization). For the pulverization (high-pressure medialess pulverization), a homogenizer (manufactured by SMT Co., Ltd., product name "UH-50") was used, and 1.85 g of the gel-like compound and 1.15 g of IPA from mixture D were weighed into a 5 cc screw bottle, and pulverization was performed at 50 W, 20 kHz for 2 minutes. This grinding process pulverized the gel-like silicon compound in the above-mentioned mixture D, resulting in the mixture D becoming a sol solution E of the pulverized material. Furthermore, to 0.75 g of sol solution E, 0.062 g of a 1.5 wt% MEK (methyl ethyl ketone) solution of a photobase generator (Wako Pure Chemical Industries, Ltd.: product name WPBG266) and 0.036 g of a 5% MEK solution of bis(trimethoxysilyl)hexane were added to obtain a coating solution for forming an intermediate layer.

[0060] [Manufacturing Example 2] Fabrication of the first light guide means A laminate (Covestro, "Bayfol® HX200") having the configuration of a TAC film / photopolymer layer / removably attached surface protective film was irradiated with laser light with a peak wavelength of 532 nm as shown in Figure 3, and a refractive index distribution corresponding to the light intensity distribution of the interference fringes of the laser light was formed at a predetermined position in the photopolymer layer. At this time, the light intensity of the laser light was 20 mJ / cm². 2 In Figure 3, the angle θ between the optical axis B1c of the first laser beam B1 and the optical axis B2c of the second laser beam B2 was set to 130 degrees. Next, ultraviolet light was irradiated onto the entire surface of the photopolymer layer from a xennon light source to cure the monomers contained in the photopolymer layer, and a refractive index distribution corresponding to the light intensity distribution of the interference fringes was fixed as a hologram. In this way, a hologram that diffracts green light was formed on the TAC film (corresponding to the first light guiding means).

[0061] A hologram that diffracts red light was formed on a TAC film (corresponding to the first light guide) in the same manner as described above, except that a laser beam with a peak wavelength of 640 nm was used. Furthermore, a hologram that diffracts blue light was formed on a TAC film (corresponding to the first light guide) in the same manner as described above, except that a laser beam with a peak wavelength of 460 nm was used.

[0062] After peeling off the surface protective film from the laminates containing the TAC film / red diffraction hologram, TAC film / green diffraction hologram, and TAC film / blue diffraction hologram obtained as described above, each was laminated with an adhesive. In this way, the first light guiding means shown in Figures 1 and 2 was fabricated.

[0063] [Manufacturing Example 3] Fabrication of the second light guide means In the same manner as in Manufacturing Example 2, a first hologram and a second hologram that diffract green light were formed at predetermined positions on the "HX200" (essentially a TAC film) used in Manufacturing Example 2. Furthermore, laminates were fabricated in the same manner as in Manufacturing Example 2, in which a first hologram and a second hologram that diffract red light were formed at predetermined positions on the TAC film, and in which a first hologram and a second hologram that diffract blue light were formed at predetermined positions on the TAC film. After peeling off the surface protective film from the laminates obtained in this way, each containing the TAC film / red diffracting first hologram and red diffracting second hologram, the TAC film / green diffracting first hologram and green diffracting second hologram, and the TAC film / blue diffracting first hologram and blue diffracting second hologram, they were laminated together with an adhesive. At this time, the first holograms of each laminate were laid in corresponding positions. In this way, the second light guiding means shown in Figures 1 and 2 was fabricated.

[0064] [Example 1] In the second light guide obtained in Manufacturing Example 3, the intermediate layer forming coating solution obtained in Manufacturing Example 1 was applied to the position of the first hologram, and after drying, the first light guide obtained in Manufacturing Example 2 was placed via the coating film. Then, ultraviolet light (wavelength 360 nm) was applied at an integrated light intensity of 350 mJ / cm². 2 The material was irradiated to crosslink the particles of the condensate of the raw material containing alkoxysilane in the coated film, forming an intermediate layer, and the first and second light guiding means were then laminated. The thickness of the intermediate layer was 2 μm, and the refractive index was 1.19. In this way, a light guiding member as shown in Figures 1 and 2 was obtained.

[0065] As is clear from the above embodiment, the light guide member of the embodiment does not need to be positioned (essentially fitted) into the housing of the wearable display while aligning the first light guide means and the second light guide means. Therefore, the manufacturing efficiency of the light guide member itself is excellent. Furthermore, since the precisely aligned light guide member only needs to be introduced into the wearable display, the manufacturing efficiency of the wearable display can also be improved. In addition, since the first light guide means and the second light guide means are laminated (bonded) in a precisely aligned state, the positional relationship between the first light guide means and the second light guide means can be maintained. Therefore, it can be seen that when the light guide member is applied to an image display device, the deterioration of image quality over time can be suppressed. [Industrial applicability]

[0066] The light guide member according to the embodiment of the present invention can be suitably used in image display devices, and in particular suitably used in wearable display devices that can be worn by a viewer. Typical examples of wearable displays include augmented reality glasses and head-mounted displays (HMDs). [Explanation of Symbols]

[0067] 10 First light guiding means 12 Holograms 20 Second light guiding means 22. Hologram 1 24. Second Hologram 30 Middle Class 50 sighted people 52 The eye of the observer 100 Light guide member 120 Image generation device 121 Image forming apparatus 122 Collimated Optics 130 Reflective spatial light modulation device 131 Liquid crystal display device 132 Polarizing Beam Splitter 140 light source 200 Image Display Devices 300 head-mounted displays

Claims

1. A first light guiding means into which light is incident, guided, and emitted; a second light guiding means into which light emitted from the first light guiding means is incident, guided, and emitted; The first light guiding means and the second light guiding means each include a diffraction grating, The first light guiding means and the second light guiding means are laminated with an intermediate layer in between. The refractive index n3 of the intermediate layer is lower than the refractive index n1 of the first light guide means and the refractive index n2 of the second light guide means, Light guide component.

2. The light guide member according to claim 1, wherein the refractive index n1 of the first light guide means, the refractive index n2 of the second light guide means, and the refractive index n3 of the intermediate layer satisfy the following relationship: n3 / n1≦0.90 n3 / n2≦0.

90.

3. The light guide member according to claim 2, wherein the refractive index n3 of the intermediate layer is 1.30 or less.

4. The light guide member according to claim 3, wherein the intermediate layer is a porous layer.

5. The light guide member according to claim 1, wherein the diffraction grating is a reflective volume hologram.

6. An image display device that can be worn by a viewer, The device comprises an image generating apparatus and a light guide member according to any one of claims 1 to 5, Light emitted from the image generation device enters the first light guide means, The second light guide means emits light toward the viewer's pupil. Image display device.

7. The image display device according to claim 6, which is an AR glasses or a head-mounted display.

Images