A glass substrate for a light guide plate, a light guide plate having a diffraction grating on the surface of the glass substrate, and a display equipped with the light guide plate.

Abstract

To provide a light guide plate glass substrate which makes it easier to obtain high image quality, a light guide plate, and a display.SOLUTION: Provided are: a disk-shaped light guide plate glass substrate made of glass having a refractive index nd of 1.90 or greater and a Young's modulus of 100 Gpa or greater; a light guide plate having a diffraction grating provided on a surface of the light guide plate glass substrate thereof; and a display with the light guide plate.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a glass substrate for a light guide plate, a light guide plate provided with a diffraction grating on the surface of the glass substrate for the light guide plate, and a display provided with the light guide plate.

Background Art

[0002] In recent years, head-mounted displays that are worn on the human head and allow the wearer to visually recognize personal images, and wearable computers using the same, have been developed. As described in Patent Document 1, a glass light guide plate is used in a head-mounted display. A head-mounted display including a light guide plate made of optical glass having a high refractive index and a low specific gravity has excellent immersion due to a wide viewing angle, and can be used in combination with an information terminal, or used for providing AR (Augmented Reality), or used as an image display device for providing movie viewing, games, VR (Virtual Reality), etc. It is suitable.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the display is operating, light repeatedly undergoes total internal reflection inside the light guide plate. The higher the refractive index of the glass, the smaller the critical angle on the surface of the light guide plate, and the larger the viewing angle of the display can be. Therefore, it is desirable to use glass with a high refractive index for the light guide plate.

[0005] By the way, when the refractive index of the glass increases, higher precision is required for the formation accuracy of the diffraction grating formed on the surface of the light guide plate.

[0006] The formation of diffraction gratings, which require fine precision, can be carried out, for example, using semiconductor device manufacturing equipment, with a glass substrate (glass wafer) for light guide plates. For example, when forming a diffraction grating on a light guide plate using lithography technology, if the glass substrate for the light guide plates, which will be used to create multiple light guide plates, is even slightly warped, the processing accuracy of the diffraction grating will decrease. Light guide plates are thin plates, and the thickness of glass wafers is also very thin, about 0.5 mm.

[0007] In order to keep such thin sheets flat, it is necessary to increase the Young's modulus of the glass material used for the glass wafer.

[0008] If the refractive index of the light guide plate glass is high, the image quality is more likely to deteriorate due to slight bending of the light guide plate when the display is in use.

[0009] In view of the above, the present invention aims to provide a glass substrate for a light guide plate, a light guide plate, and a display equipped therewith, which can form a diffraction grating with high processing accuracy using lithography technology, and which also have a wide viewing angle and can easily obtain high image quality. [Means for solving the problem]

[0010] As a result of diligent research, the inventors of this invention have discovered that the above problems can be solved by using a glass substrate made of high refractive index, high Young's modulus glass, and have completed this invention. This invention encompasses the following: [1] A glass substrate for a light guide plate, having a disc shape, a refractive index nd of 1.90 or higher, and a Young's modulus of 100 GPa or higher. [2] A glass substrate for a light guide plate according to [1], wherein the main surface is divided into multiple sections, and each section is provided with a light guide path. [3] A light guide plate made of glass having a refractive index nd of 1.90 or higher and a Young's modulus of 100 GPa or higher. [4] A display equipped with the light guide plate described in [3]. [Effects of the Invention]

[0011] According to one embodiment of the present invention, it is possible to provide a glass substrate for a light guide plate, a light guide plate, and a display equipped therewith, which have a wide viewing angle and can easily obtain high image quality. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1(a) is a plan view of the glass wafer 1, and Figure 1(b) is a side view of the glass wafer 1. Virtual circles A and B are shown.

[0013] (light guide plate) One embodiment of the present invention is a light guide plate made of glass having a refractive index nd of 1.90 or higher and a Young's modulus of 100 GPa or higher. Since the above light guide plate has a refractive index nd of 1.90 or higher, using it as a light guide plate for displays such as head-mounted displays can increase the field of view. The preferred range for the refractive index nd is 1.92 or higher, a more preferred range is 1.94 or higher, an even more preferred range is 1.96 or higher, an even more preferred range is 1.98 or higher, and an even more preferred range is 2.00 or higher. There is no particular upper limit to the preferred refractive index nd, but 2.5 or lower can be used as a guideline.

[0014] The light guide plate described above has a Young's modulus of 100 GPa or higher. Having a Young's modulus of 100 GPa or higher allows for higher processing accuracy, such as the formation of diffraction gratings using lithography techniques with semiconductor devices, and also suppresses the degradation of image quality due to warping or bending of the light guide plate. The preferred range for Young's modulus is 105 GPa or higher, more preferably 110 GPa or higher, even more preferably 115 GPa or higher, and even more preferably 120 GPa or higher. There is no particular upper limit to the Young's modulus, but it can be used as a guideline to keep it below 180 GPa.

[0015] The glass used in the light guide plate is preferably optically homogeneous optical glass. Furthermore, it is preferable that the glass has high transmittance in the visible spectrum.

[0016] The specific gravity of the glass used for the light guide plate is preferably 4.4 to 5.4. Regarding the degree of coloring of the glass used for the light guide plate, λ70 is preferably 420 nm or less, and λ5 is preferably 380 nm or less. Further, the external transmittance at a wavelength of 400 nm converted to a plate thickness of 10 mm is preferably 60% or more, and more preferably 70% or more.

[0017] Regarding the composition of the glass, there is no particular limitation as long as the desired properties can be obtained. However, from the viewpoint of stably supplying high-quality glass, glass containing B2O3 and La2O3 as glass components is preferable.

[0018] (Glass substrate for light guide plate) One embodiment of the present invention is a glass substrate for a light guide plate made of glass having a disk shape, a refractive index nd of 1.90 or more, and a Young's modulus of 100 GPa or more. By cutting such a glass substrate for a light guide plate, a plurality of light guide plates 5 can be provided simultaneously. The cut light guide plates can be used as they are as light guide plates, or can be used after polishing or adding functions.

[0019] An example of a glass substrate for a light guide plate (hereinafter sometimes referred to as a glass wafer) is shown in FIG. 1. FIG. 1(a) is a plan view of the glass wafer 1, and FIG. 1(b) is a side view of the glass wafer 1. The circle in FIG. 1(a) is the outline of the glass wafer 1, and the straight lines arranged in a grid pattern inside this circle are virtual lines 2. Also, the rectangle in the side view of FIG. 1(b) is the outline of the glass wafer 1, and the straight line parallel to the short side of the inner rectangle of the rectangle is also a virtual line 2.

[0020] The glass wafer 1 has main surfaces 31 and 32. When at least one of the main surfaces 31 and 32 is partitioned into a plurality by virtual lines 2, each partition is provided with a light guide path (not shown). By providing such a light guide path, when the glass wafer 1 is cut along the virtual line 2 as will be described later, each glass piece 4 can be used as a light guide plate.

[0021] By using a cutting machine, such as a dicing machine, etc., to cut the virtual line 2 of the glass wafer 1, glass pieces 41 and 42 can be made. Note that the glass piece 41 is the outermost glass piece forming the side surface of the glass wafer 1, and the plurality of glass pieces 42 are surrounded by the glass piece 41 and are in a state of being most densely packed with a rectangular or square planar shape. The obtained glass piece 42 can be used as a light guide plate 5. Therefore, in the glass wafer 1, the virtual line 2 becomes the boundary of each light guide plate 5. As described above, by cutting the boundary of the glass wafer 1, a large number of light guide plates 5 can be made from a single glass wafer 1.

[0022] In order to make a large number of glass pieces 41 (light guide plates 5) at once, the glass wafer 1 may be cut or divided so that a large number of glass pieces 41 are formed on a glass wafer 1 with a large diameter. By using the glass wafer 1 having the above characteristics, the warpage and deflection of the wafer are extremely small, so that a diffraction grating with high precision can be formed on each light guide plate 5.

[0023] The glass wafer 1 can be manufactured, for example, as follows. First, a glass raw material is prepared to have the required composition, the prepared raw material is heated and melted, and the molten glass is homogenized, clarified and formed. After the formed glass is slowly cooled, it is processed into a disk shape using a known processing method.

[0024] For example, the plate thickness of the glass wafer 1 processed into a disk shape is 0.2 to 3 mm, the diameter is 150 to 450 mm, the TV (total thickness variation) is within 1 μm, the arithmetic mean roughness Ra of both main surfaces is 0.5 nm or less, and the arithmetic mean roughness Ra of the side surface is 100 μm or less. Note that TTV is the difference between the maximum value and the minimum value of the thickness of the substrate. From a single glass wafer 1, 5 to 20 light guide plates 5 can be formed.

[0025] When viewing the cut glass fragments 41 from above, assuming a hypothetical circle A inscribed in the contour line and a hypothetical circle B circumscribed around the planar shape of each glass fragment 41 (see Figure 1(c)), the diameter of circle A is 30 mm or more, and the diameter of circle B is 150 mm or less. As a method for manufacturing the glass wafer 1, molten glass may be directly formed into a disc shape. Alternatively, a disc-shaped glass wafer 1 can be manufactured by forming molten glass into a cylindrical shape and then slicing it. Another manufacturing method involves joining or bonding columnar glass pieces with relatively small cross-sectional areas to each other to create a bundle of columnar glass pieces, then shaping it into a cylinder and cutting it to produce a disc-shaped glass wafer 1. In this manufacturing method, line 2 represents the lines formed by joining the glass pieces together.

[0026] (display) One aspect of the present invention is a display equipped with the above-mentioned light guide plate. The display of the present invention is not particularly limited as long as it is equipped with the light guide plate of the present invention. A specific example of the display is a head-mounted display worn on a human head. That is .

[0027] In a head-mounted display, the light guide plate of the present invention is positioned in front of the right and left eyes. Light emitted from signal processing devices and display units located inside or outside the head-mounted display is refracted inside the light guide plate and transmitted to form an image on the wearer's right and left eye retinas.

[0028] Since the air-equivalent optical path length of light traveling through the light guide plate decreases with increasing refractive index, using the optical glass according to this embodiment, which has a high refractive index, allows for a larger apparent viewing angle. Furthermore, because the specific gravity is kept low despite the high refractive index, a lightweight display that achieves the above effects can be provided. In addition, if the Young's modulus is high and the warping and bending are extremely small, accurate optical information can be transmitted.

[0029] Furthermore, a light guide plate according to one aspect of the present invention can be used in see-through, transmissive, or opaque head-mounted displays. [Examples]

[0030] Glass raw materials were prepared to obtain glass exhibiting the composition and optical properties described in Table 1. The prepared raw materials were heated, melted, homogenized, and clarified. The mixture was then poured into a mold to form plate-shaped glass, which was slowly cooled. None of the plate-shaped glass samples showed crystal precipitation or striations, and were optically homogeneous.

[0031] The refractive index nd was measured for each glass sample that was slowly cooled at a cooling rate of 30°C / hour, using the refractive index measurement method specified in JIS B 7071-1. The refractive index ng, nF, and nC were measured similarly, and the Abbe number νd was calculated based on the following formula. νd=(nd-1) / (nF-nC)

[0032] The degree of coloration λ70 and λ5 was measured using the following method.

[0033] [Table 1]

[0034] Each of the above-mentioned glass samples was processed to have a thickness of 10 mm and parallel, optically polished surfaces, and its spectral transmittance was measured in the wavelength range from 280 nm to 700 nm. The intensity of light rays incident perpendicularly to one of the optically polished surfaces was defined as intensity A, and the intensity of light rays emanating from the other surface was defined as intensity B, and the spectral transmittance B / A was calculated. The wavelength at which the spectral transmittance was 70% was defined as λ70, and the wavelength at which the spectral transmittance was 5% was defined as λ5. Note that the spectral transmittance includes the reflection loss of light rays at the glass surface.

[0035] Young's modulus was measured using the ultrasonic method, and specific gravity was measured using the Archimedes method.

[0036] The internal transmittance at a wavelength of 400 nm, calculated for a 10 mm thickness, is a value that excludes the reflection loss of light rays at the glass surface.

[0037] Next, the flat glass was machined to produce numerous glass wafers with a thickness of 0.5 mm and a diameter of 300 mm.

[0038] The arithmetic mean roughness Ra of both main surfaces of the glass wafer was 0.5 nm or less, and the TTV of the substrate was within 1 μm.

[0039] Next, a coating was applied to a glass wafer using semiconductor manufacturing equipment, and a diffraction grating was formed at the light emission position to create a light guide plate. Then, each light guide plate was separated using a dicing machine to obtain multiple light guide plates.

[0040] These light guide plates were incorporated into a head-mounted display to show images. The display had a wide viewing angle and achieved high image quality.

[0041] (Comparative example) A light guide plate with a diffraction grating was fabricated using glass with a Young's modulus of 90 GPa, and incorporated into a head-mounted display to display an image. Due to the low Young's modulus, it was not possible to form a high-precision diffraction grating, and the light guide plate deformed slightly due to the force applied when it was incorporated into the display, resulting in a decrease in image quality.

[0042] According to the present invention, it is possible to provide a glass substrate for a light guide plate, a light guide plate, and a display that have a wide viewing angle and can easily obtain high image quality.

Claims

1. A glass substrate for a light guide plate, having a disc shape, a refractive index nd of 1.94 or higher, and a Young's modulus of 115 GPa or higher, wherein the internal transmittance at a wavelength of 400 nm, calculated for a 10 mm thickness of the glass, is 77.9% or higher.

2. A glass substrate for a light guide plate, having a disc shape, a refractive index nd of 1.94 or higher, and a Young's modulus of 115 GPa or higher, wherein the degree of coloration λ70 of the glass is 420 nm or less, and the degree of coloration λ5 is 380 nm or less.

3. A glass substrate for a light guide plate according to claim 1 or 2, comprising glass having a refractive index nd of 1.98 or higher and a Young's modulus of 120 GPa or higher.

4. The glass substrate for a light guide plate according to claim 1, wherein the degree of coloration of the glass λ70 is 420 nm or less, and the degree of coloration of λ5 is 380 nm or less.

5. The aforementioned glass component is B ２ O ３ and La ２ O ３ A glass substrate for a light guide plate according to claim 1 or 2, comprising the above.

6. The glass substrate for a light guide plate according to claim 1 or 2, wherein the main surface is divided into multiple sections, and each section is provided with a light guide path.

7. A light guide plate made of glass having a refractive index nd of 1.94 or more and a Young's modulus of 115 GPa or more, wherein the internal transmittance at a wavelength of 400 nm, calculated for a thickness of 10 mm in the glass, is 77.9% or more.

8. A light guide plate made of glass having a refractive index nd of 1.94 or more and a Young's modulus of 115 GPa or more, wherein the degree of coloration λ70 of the glass is 420 nm or less and the degree of coloration λ5 is 380 nm or less.

9. The light guide plate according to claim 7 or 8, comprising glass having a refractive index nd of 1.98 or more and a Young's modulus of 120 GPa or more.

10. The light guide plate according to claim 7, wherein the degree of coloration of the glass λ70 is 420 nm or less and the degree of coloration of λ5 is 380 nm or less.

11. The light guide plate according to claim 7 or 8, wherein the glass contains B2O3 and La2O3 as components.

12. A display comprising the light guide plate according to claim 7 or 8.

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