Light guide plate

Abstract

To provide a light guide plate capable of increasing color reproducibility of an image when used as a light guide plate for a spectacles-type device such as an AR / MR wearable device.SOLUTION: A light guide plate 10 comprises a glass plate 1 and a resin layer 2 formed on a main surface of the glass plate 1, and in the light guide plate 10, a difference in Abbe number νd between the glass plate 1 and the resin layer 2 is less than 10 and refractive index nd of the glass plate 1 and the resin layer 2 is 1.7 or greater and the difference is 1.0 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a light guide plate used in glasses-type devices such as wearable devices for AR (augmented reality) / MR (mixed reality). [Background technology]

[0002] In recent years, glasses-type devices such as wearable devices for AR / MR have been developed. These glasses-type devices are see-through devices that allow users to view images displayed on a light guide plate in the glasses while looking at the outside scenery. Such see-through devices can achieve 3D display by displaying different images on light guide plates corresponding to the user's left and right eyes, or can project images directly onto the user's retina by using the crystalline lens in the eye to combine images onto the retina.

[0003] One method of displaying images using a light guide plate involves using a diffraction grating formed on the light-incident surface of the light guide plate to allow collimated light or laser light emitted from an image display element to enter the light guide plate, guiding the incident light while causing total reflection inside the light guide plate, and then extracting the light to the outside using a diffraction grating formed on the light-exiting surface, allowing it to enter the user's pupil.A light guide plate has been proposed in which the surface of a glass plate with a high refractive index and excellent rigidity is coated with a resin, and then a high-resolution diffraction grating is formed by nanoimprinting (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-8599 Summary of the Invention [Problem to be solved by the invention]

[0005] When a light guide plate made of a resin-coated glass plate is used in glasses-type devices such as wearable devices for AR / MR, it may not be possible to project images with good color reproducibility.

[0006] In view of the above, an object of the present invention is to provide a light guide plate that can improve the color reproducibility of images when used as a light guide plate for glasses-type devices such as wearable devices for AR / MR. [Means for solving the problem]

[0007] The light guide plate of the present invention is a light guide plate comprising a glass plate and a resin layer formed on a main surface of the glass plate, characterized in that the difference in Abbe number νd between the glass plate and the resin layer is less than 10, and the refractive indexes nd of the glass plate and the resin layer are 1.7 or more and the difference is 1.0 or less.

[0008] The light guide plate of the present invention comprises a glass plate and a resin layer, each of which has a refractive index appropriate for its material. A small difference in the refractive index between the glass plate and the resin layer can suppress light scattering at the interface between them. However, because the refractive index of each material is wavelength-dependent, the difference in refractive index may vary depending on the wavelength. For example, even if the difference in refractive index between the glass plate and the resin layer is small at one wavelength, thereby suppressing light scattering at the interface, the difference in refractive index between the glass plate and the resin layer may be large at another wavelength, resulting in significant light scattering at the interface. Therefore, the inventors focused on the Abbe number νd, which is an index of refractive index wavelength dependence, and found that the above-mentioned problem can be solved by reducing the difference in Abbe number νd between the glass plate and the resin layer as described above. Specifically, reducing the difference in Abbe number νd between the glass plate and the resin layer reduces the difference in the slope of the refractive index wavelength-dependence curves between the two, thereby reducing the variation in the refractive index difference at each wavelength. As a result, light scattering at the interface between the two at each wavelength can be suppressed. This improves the color reproducibility of images. Furthermore, in the light guide plate of the present invention, the difference in refractive index nd between the glass plate and the resin layer is 1.0 or less, so that the difference in refractive index between the glass plate and the resin layer is small, making it difficult for light scattering loss to occur at the interface between the two.

[0009] In the light guide plate of the present invention, the thickness of the glass plate is preferably 0.1 to 1 mm, and the thickness of the resin layer is preferably 1 μm or less. The intensity of light incident on the light guide plate is reduced mainly due to light scattering loss caused by the difference in refractive index at the interface between the glass plate and the resin layer, and loss due to absorption within the glass plate or resin layer. When the thickness of the glass plate or resin layer is small, the absorption loss within them tends to be small, and the influence of light scattering loss at the interface between the glass plate and the resin layer tends to be relatively large. Therefore, when the thickness of the glass plate or resin layer is small as described above, the effects of the present invention can be easily achieved.

[0010] The light guide plate of the present invention preferably has an internal transmittance of 70% or more at a wavelength of 450 to 650 nm when the glass plate has a thickness of 10 mm, thereby reducing absorption loss when light is guided inside the glass plate and increasing the intensity of the emitted light.

[0011] The light guide plate of the present invention preferably has a difference in external transmittance between wavelengths of 450 nm and 650 nm of 5% or less, which reduces the variation in light output intensity from the light guide plate depending on wavelength, and tends to improve the color reproducibility of images.

[0012] In the light guide plate of the present invention, the main surfaces of the glass plates preferably have a surface roughness Ra of 5 nm or less, which can suppress light scattering loss on the main surfaces of the glass plates when light is reflected and guided between the main surfaces of the glass plates, thereby increasing the intensity of the emitted light.

[0013] In the light guide plate of the present invention, it is preferable that an uneven structure is formed on the surface of the resin layer, so that the resin layer functions as a diffraction grating, allowing external light to enter the glass plate and light inside the glass plate to exit the glass plate.

[0014] In the light guide plate of the present invention, the resin layer is preferably made of a photocurable resin, which makes it possible to easily obtain a concave-convex structure having a nano-order shape.

[0015] The wearable device for AR / MR of the present invention is characterized by including any one of the light guide plates described above. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a light guide plate that can improve the color reproducibility of images when used as a light guide plate for glasses-type devices such as AR / MR wearable devices. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view showing an embodiment of a light guide plate of the present invention. [Figure 2] 10 is a graph showing transmittance curves of the light guide plate and glass plate of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the light guide plate of the present invention will be described with reference to the drawings.

[0019] FIG. 1 is a schematic cross-sectional view showing one embodiment of a light guide plate of the present invention. Light guide plate 10 includes a glass plate 1 and a resin layer 2. Resin layer 2 is composed of resin layers 2a and 2b, each of which is formed on one main surface of glass plate 1. Specifically, resin layer 2a is formed on the surface of the light input portion of glass plate 1, and resin layer 2b is formed on the surface of the light output portion of glass plate 1. An uneven structure is formed on the surfaces of resin layers 2a and 2b, which functions as a diffraction grating.

[0020] Light emitted from an image display element (not shown) enters the light guide plate 10 as incident light L1. The incident light L1 is diffracted by the resin layer 2a and enters the interior of the glass plate 1. The incident light L1 is guided through the interior of the glass plate 1 to the light exit portion while being totally reflected between both main surfaces of the glass plate 1. The incident light L1 is diffracted by the resin layer 2b formed in the light exit portion and is emitted to the outside of the glass plate 1 as exit light L2, which enters the human eye. In this way, the image projected from the image display element can be viewed. Furthermore, since the light guide plate 1 itself is transparent and see-through, the outside scenery can also be viewed through the light guide plate 1. The incident light L1 and exit light L2 are visible light, for example, light with a wavelength in the range of 400 to 800 nm.

[0021] (Glass plate 1) The refractive index (nd) of the glass plate 1 is 1.7 or more, preferably 1.8 or more, 1.9 or more, 1.95 or more, and particularly preferably 1.98 or more. On the other hand, the upper limit of the refractive index of the glass plate 1 is preferably 2.1 or less, 2.05 or less, 2.03 or less, and particularly preferably 2.01 or less. If the refractive index of the glass plate 1 is too low, the field of view (FOV) tends to be narrow when used as a light guide plate for a wearable device for AR / MR, etc. On the other hand, if the refractive index is too high, defects such as devitrification and striae occur, and the internal transmittance is likely to decrease.

[0022] The Abbe number of the optical glass 1 is not particularly limited. However, since many resins with a refractive index of 1.7 or more have an Abbe number of 30 or less, from the viewpoint of reducing the difference in Abbe number with the resin layer 2, the lower limit of the Abbe number of the optical glass 1 is preferably 20 or more, 22 or more, and particularly 25 or more, and the upper limit is preferably 30 or less, and particularly 28 or less.

[0023] The thickness of the glass plate 1 is preferably 0.1 mm or more, 0.15 mm or more, particularly 0.2 mm or more, and is preferably 1 mm or less, 0.5 mm or less, 0.4 mm or less, particularly 0.3 mm or less. If the thickness of the glass plate 1 is too small, the mechanical strength is likely to decrease. On the other hand, if the thickness of the glass plate 1 is too large, the weight of a wearable device using the glass plate 1 increases, which tends to increase discomfort when wearing the device.

[0024] The length of the major axis (diagonal in the case of a rectangle) of the main surface of the glass plate 1 is preferably 100 mm or less, 80 mm or less, and particularly 50 mm or less. This allows for miniaturization of the wearable device. There is no particular lower limit, but in reality it is 10 mm or more, particularly 300 mm or more.

[0025] It should be noted that the more compact the glass plate 1 (the smaller the thickness and major axis), the shorter the optical path length when light is guided inside the glass plate 1, which reduces internal absorption loss and tends to relatively increase the effect of light scattering loss at the interface between the glass plate 1 and the resin layer 2. Therefore, when the thickness of the glass plate 1 is small as described above, it becomes easier to enjoy the effects of the present invention.

[0026] The internal transmittance of the glass plate 1 at a thickness of 10 mm at wavelengths of 450 to 650 nm is preferably 70% or more, 80% or more, 90% or more, particularly preferably 95% or more. This can suppress absorption loss when light is guided inside the glass plate 1, and can increase the intensity of the emitted light.

[0027] The surface roughness Ra of the first principal surface 1a and the second principal surface 1b of the glass plate 1 is preferably 5 nm or less, 3 nm or less, and particularly preferably 2 nm or less. If the surface roughness Ra of the first principal surface 1a and the second principal surface 1b of the glass plate 1 is too large, scattering loss is likely to occur when light incident on the interior of the glass plate 1 is guided through repeated total reflections, making it difficult to obtain a bright, clear image. There is no particular lower limit to the surface roughness Ra of the first principal surface 1a and the second principal surface 1b of the glass plate 1, but in practice it is 0.1 nm or more.

[0028] The difference between the maximum and minimum distances between the first and second main surfaces 1a and 1b of the glass plate 1 (TTV = Total Thickness Variation) is preferably 5 μm or less, 3 μm or less, and particularly preferably 1 μm or less. If the TTV is too large, it becomes difficult for light of each wavelength incident on the glass plate 1 to be accurately guided within the glass plate 1, and the clarity of the resulting image is likely to decrease.

[0029] The glass composition of the glass plate 1 preferably contains SiO2 and B2O3, which are components that improve the stability of vitrification, and La2O3 and Nb2O5, which are components that increase the refractive index. By containing these components, it becomes easier to obtain glass that has a high refractive index and is easy to mass-produce.

[0030] The preferred range of each component will be explained below. In the following explanation, "%" means "% by mass" unless otherwise specified.

[0031] SiO2 is effective for vitrification, but is also a component that significantly lowers the refractive index, so the SiO2 content is preferably 1 to 45%, particularly 3 to 35%.

[0032] Although B2O3 is effective for vitrification, it is a component that increases the Abbe number, so if the content is too high, it becomes difficult to obtain the desired Abbe number (for example, 30 or less). Therefore, the B2O3 content is preferably 10% or less, and particularly 9.5% or less. There is no particular lower limit, but in order to improve the stability of vitrification, it is preferably 1% or more, and particularly 2% or more.

[0033] The content of SiO2+B2O3 is preferably 1 to 55%, and more preferably 5 to 40%. In this specification, "x+y+···" means the total amount of each component.

[0034] La2O3 is a component that significantly increases the refractive index and improves the stability of vitrification. The La2O3 content is preferably 0 to 60%, 10 to 55%, 20 to 52%, and particularly preferably 30 to 50%. If the La2O3 content is too high, the devitrification resistance decreases, which tends to make mass production difficult.

[0035] Nb2O5 is a component that significantly increases the refractive index. It also has the effect of lowering the Abbe number. The content of Nb2O5 is preferably 0 to 40%, 3 to 40%, and particularly preferably 5 to 39%.

[0036] The content of La2O3+Nb2O5 is preferably 20 to 70%, particularly preferably 30 to 65%.

[0037] In addition to La2O3 and Nb2O5, Gd2O3, Y2O3 or Yb2O3 may be contained as a component for increasing the refractive index.

[0038] Like La2O3, Gd2O3 can be contained in glass at high content, but if it is too much, the glass density increases and it becomes more susceptible to devitrification. Therefore, the Gd2O3 content is preferably 0 to 20%, and more preferably 1 to 10%.

[0039] The content of Y2O3 and Yb2O3 is preferably 0 to 10%, particularly preferably 0.1 to 8%. If the content of these components is too high, devitrification tends to occur.

[0040] Increasing the content of Ln2O3 (Ln is at least one selected from La, Gd, Y, and Yb) makes it easier to achieve a desired high refractive index (for example, 1.7 or more, 1.8 or more, or even 1.9 or more). However, if the content of Ln2O3 is too high, devitrification tends to occur. Therefore, the content of Ln2O3 is preferably 40 to 65%, 45 to 63%, and particularly preferably 48 to 60%.

[0041] In addition to the above components, it is preferable to contain TiO2 and ZrO2, which contribute to improving the refractive index.

[0042] TiO2 is a component that increases the refractive index and decreases the Abbe number. The TiO2 content is preferably 5 to 40%, particularly 10 to 30%. If the TiO2 content is too low, it becomes difficult to obtain the above effects. On the other hand, if the TiO2 content is too high, the transmittance decreases and vitrification becomes unstable.

[0043] ZrO2 is also a component that increases the refractive index and decreases the Abbe number. The ZrO2 content is preferably 1 to 10%, particularly 3 to 8%. If the ZrO2 content is too low, it becomes difficult to obtain the above effects. On the other hand, if the ZrO2 content is too high, the transmittance decreases and vitrification becomes unstable.

[0044] In addition, for the purpose of improving vitrification stability, alkali metal components (Li2O, Na2O, or KO), alkaline earth metal components (MgO, CaO, SrO, or BaO), or ZnO can be contained in a total amount of 0 to 30%. The alkali metal components can be contained for the purpose of adjusting the refractive index and Abbe number. Specifically, alkali metal components tend to lower the refractive index and Abbe number. The content of the alkali components is preferably 0 to 20%.

[0045] Sb2O3 can be contained in the range of 0.1% or less for the purpose of improving clarity and transmittance.

[0046] It is preferable that As components (e.g., As2O3), Pb components (e.g., PbO), and fluorine components (e.g., F2) are not substantially contained because they have a large environmental impact. Furthermore, Bi2O3 and TeO2 are coloring components that tend to reduce transmittance in the visible range, so it is preferable that they are not substantially contained. Here, "substantially not contained" means that they are not intentionally included as raw materials, and does not exclude the inclusion of unavoidable impurities. Objectively, this means that the content of each of the above components is less than 0.1%.

[0047] Multiple glass plates 1 may be stacked together to form a laminate. In this way, when glass plate 1 is used as a light guide plate for a wearable device, it becomes possible to project images in a layered manner in the depth direction of the display screen, thereby producing 3D images. It is preferable that the number of stacked plates is three or more, and particularly six or more.

[0048] (Resin layer 2) The refractive index (nd) of the resin layer 2 is 1.7 or more, preferably 1.8 or more, 1.9 or more, 1.95 or more, and particularly preferably 1.98 or more. On the other hand, the upper limit of the refractive index of the resin layer 2 is preferably 2.1 or less, 2.05 or less, 2.03 or less, and particularly preferably 2.01 or less. This reduces the difference in refractive index between the resin layer 2 and the glass plate 1, making it less likely that light scattering loss will occur at the interface between the resin layer 2 and the glass plate 1.

[0049] The difference in refractive index (nd) between the glass plate 1 and the resin layer 2 is 1.0 or less, and preferably 0.5 or less, 0.3 or less, 0.2 or less, and particularly preferably 0.15 or less. This reduces the difference in refractive index from the glass plate 1, making it less likely that light scattering loss will occur at the interface between the glass plate 1 and the resin layer 2.

[0050] Taking into consideration the difference in Abbe number between the resin layer 2 and the optical glass 1, the Abbe number of the resin layer 2 is preferably, for example, 10 or more, 15 or more, 20 or more, and particularly 25 or more, and the upper limit is preferably 45 or less, 40 or less, 35 or less, and particularly 30 or less.

[0051] The difference in Abbe number (νd) between the glass plate 1 and the resin layer 2 is less than 10, and preferably not more than 8, not more than 5, and particularly not more than 3. By doing so, for the reasons described above, it is possible to suppress light scattering at the interface between the glass plate 1 and the resin layer 2 at each wavelength, thereby improving the color reproducibility of the image.

[0052] An example of an index of image color reproducibility is the difference in external transmittance (transmittance including reflection loss) at wavelengths of 450 nm and 650 nm of light guide plate 10, which is a laminate of glass plate 1 and resin layer 2. The difference in external transmittance at wavelengths of 450 nm and 650 nm of light guide plate 10 is preferably 5% or less, 4% or less, 3% or less, and particularly preferably 2.5% or less. This reduces variation in the light output intensity from light guide plate 10 depending on wavelength, making it easier to improve image color reproducibility.

[0053] The thickness of the resin layer 2 is preferably 5 μm or less, 1 μm or less, and particularly 0.5 μm or less. If the thickness of the resin layer 2 is too large, light absorption increases, and the intensity of light emitted from the light guide plate 10 tends to decrease. There is no particular lower limit to the thickness of the resin layer 2, but in order to form a desired uneven structure on the surface, a thickness of 0.01 μm or more, particularly 0.1 μm or more, is preferred. Note that the thinner the thickness of the resin layer 2, the smaller the absorption loss within the resin layer 2, and the greater the influence of light scattering loss at the interface between the glass plate 1 and the resin layer 2 tends to be. Therefore, when the thickness of the resin layer 2 is as small as described above, the effects of the present invention are more easily achieved.

[0054] When forming a concave-convex structure on the surface of the resin layer 2, the height thereof may be appropriately set so as to obtain a desired diffraction ability. For example, the height of the concave-convex structure may be 0.01 to 0.2 μm, or even 0.03 to 0.1 μm.

[0055] The resin layer 2 is preferably a photocurable resin, which makes it possible to easily obtain a concave-convex structure having a nano-order shape. [Example]

[0056] The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0057] Table 1 shows examples (Nos. 1 to 3) of the present invention and a comparative example (No. 4), and Table 2 shows the compositions of the glass plates used in the examples and comparative example.

[0058] [Table 1]

[0059] [Table 2]

[0060] In this example, the difference in external transmittance depending on wavelength was evaluated for a light guide plate having a resin layer formed on the surface of a glass plate having the properties and composition shown in Tables 1 and 2. Specifically, the difference in external transmittance of the light guide plate at wavelengths of 450 nm and 650 nm was measured. The glass plate was fabricated by blending raw materials to obtain the composition shown in Table 2, melting and casting the raw materials in a platinum crucible at 1250 to 1400°C in the atmosphere to obtain a glass molded body, and then cutting and polishing the glass molded body. The resin used for the resin layer had a refractive index of 1.71 to 2.10, an Abbe number of 24 to 36, and an internal transmittance of 99%. The external transmittance curve of the light guide plate of Example 2 is shown in Figure 2. For reference, Figure 2 also shows the external transmittance curve of the glass plate used in Example 2.

[0061] The surface roughness Ra of the glass plate was measured using an AFM Dimension Icon manufactured by Bruker, with a scan size of 10 μm and a scan rate of 1 Hz.

[0062] The refractive index of the glass plates was measured as follows: A 0.3 mm thick glass plate was cut or polished at a right angle, and the cut or polished surface was mirror-polished with #1000 abrasive paper. Two of the glass plates were then bonded together in a refractive index-matching immersion liquid (Kalnew) with a refractive index of 1.78, and the refractive index was measured using a Shimadzu KPR-2000. The Abbe number was calculated from the refractive indexes at the d-line, C-line, and F-line wavelengths.

[0063] The internal transmittance of the glass plates was measured as follows. Glass plates with a size of 10 x 10 mm or more and a thickness of 10 mm and a thickness of 3 mm were prepared from the glass molded body produced by the method described above, and these were mirror-polished with #1000 abrasive paper or cerium abrasive powder. The internal transmittance, excluding reflection loss, of these glass plates was calculated from the transmittance measured using a UV-3100 manufactured by Shimadzu Corporation.

[0064] The refractive index of the resin was measured using an ellipsometer EF-5000 manufactured by Otsuka Electronics Co., Ltd. The Abbe number was calculated from the refractive index at each wavelength of the d-line, C-line, and F-line obtained.

[0065] The transmittance of the light guide plate, which was formed by forming a resin layer on the surface of a glass plate, was measured using UV-3100 manufactured by Shimadzu Corporation.

[0066] As shown in Table 1, the light guide plates of Examples 1 to 3 had a small difference in Abbe number between the glass plate and the resin layer of 8 or less, and a small difference in transmittance at wavelengths of 450 nm and 650 nm of 2%. Therefore, it is believed that they will have high color reproducibility when used as light guide plates for wearable AR / MR devices. On the other hand, the light guide plate of Comparative Example No. 4 had a large difference in Abbe number between the glass plate and the resin layer of 11, and a large difference in transmittance at wavelengths of 450 nm and 650 nm of 7%. Therefore, it is believed that they will have poor color reproducibility when used as light guide plates for wearable AR / MR devices.

Claims

1. A light guide plate comprising a glass plate and a resin layer formed on a main surface of the glass plate, the difference in Abbe number νd between the glass plate and the resin layer is less than 10; The glass plate contains, by mass %, 0 to 2% of Li 2 O and 0 to 10% of B 2 O 3 ; A light guide plate, characterized in that the refractive indexes nd of the glass plate and the resin layer are 1.7 or more and the difference between them is 1.0 or less.

2. 2. The light guide plate according to claim 1, wherein the glass plate has a thickness of 0.1 to 1 mm, and the resin layer has a thickness of 1 μm or less.

3. 3. The light guide plate according to claim 1, wherein the internal transmittance of the glass plate at a thickness of 10 mm in the wavelength range of 450 to 650 nm is 70% or more.

4. 4. The light guide plate according to claim 1, wherein the difference in external transmittance between wavelengths of 450 nm and 650 nm is 5% or less.

5. 5. The light guide plate according to claim 1, wherein the main surface of the glass plate has a surface roughness Ra of 5 nm or less.

6. 6. The light guide plate according to claim 1, wherein an uneven structure is formed on the surface of the resin layer.

7. 7. The light guide plate according to claim 1, wherein the resin layer is made of a photocurable resin.

8. A wearable device for AR / MR, comprising the light guide plate according to any one of claims 1 to 7.

Images