JP2023149632A - Light guide plate glass substrate, light guide plate with diffraction grating on surface of the same, and display with light guide plate - Google Patents

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

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.

In recent years, head-mounted displays that are attached to the human head and allow the wearer to view personal images, and wearable computers that utilize these displays have been developed. As described in Patent Document 1, a head-mounted display uses a glass light guide plate. A head-mounted display equipped with a light guide plate made of optical glass with a high refractive index and low specific gravity has an excellent immersive feeling due to its wide viewing angle, and can be used in combination with information terminals and provides services such as AR (Augmented Reality). The image display device is suitable for use as an image display device for personal use, watching movies, playing games, providing VR (Virtual Reality), and the like.

Japanese Patent Application Publication No. 2016-139174

When a display is in operation, light travels through the light guide plate through repeated total reflection, but the higher the refractive index of glass, the smaller the critical angle on the light guide plate surface, making it possible to increase the viewing angle of the display. Therefore, it is desirable to use glass with a high refractive index for the light guide plate.

Incidentally, as the refractive index of glass increases, the formation precision of the diffraction grating formed on the surface of the light guide plate is also required to be higher.

Formation of a diffraction grating that requires fineness and high precision can be performed using a glass substrate for a light guide plate (glass wafer), for example, using a semiconductor device manufacturing apparatus. For example, when forming a diffraction grating on a light guide plate using a lithography technique, if the glass substrate for the light guide plate from which a plurality of light guide plates are manufactured is even slightly warped, the processing accuracy of the diffraction grating will be reduced. The light guide plate is a thin plate, and the thickness of the glass wafer is also very thin, about 0.5 mm.

In order to keep such a thin plate flat, it is necessary to increase the Young's modulus of the glass that is the material of the glass wafer.

When the refractive index of the glass of the light guide plate is high, image quality tends to deteriorate due to slight bending of the light guide plate when the display is used.

In view of the above, the present invention provides a glass substrate for a light guide plate, a light guide plate, and a display including the same, which allows a diffraction grating to be formed with high processing precision using lithography technology, has a large viewing angle, and makes it easy to obtain high image quality. The purpose is to provide.

As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by using a glass substrate made of glass with a high refractive index and a high Young's modulus, and have completed the present invention. The present invention includes the following.
[1] A glass substrate for a light guide plate made of glass having a disc shape, a refractive index nd of 1.90 or more, and a Young's modulus of 100 GPa or more.
[2] The glass substrate for a light guide plate according to [1], wherein the main surface is divided into a plurality of 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 more and a Young's modulus of 100 GPa or more.
[4] A display comprising the light guide plate according to [3].

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 including the same, which has a large viewing angle and which makes it easy to obtain high image quality.

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. A virtual circle A and a virtual circle B are shown.

(Light guide plate)
One form of the present invention is a light guide plate made of glass having a refractive index nd of 1.90 or more and a Young's modulus of 100 GPa or more.
Since the light guide plate has a refractive index nd of 1.90 or more, when used as a light guide plate for a display such as a head-mounted display, the viewing angle can be increased. The preferable range of the refractive index nd is 1.92 or more, the more preferable range is 1.94 or more, the even more preferable range is 1.96 or more, the even more preferable range is 1.98 or more, and the even more preferable range is 2.00 or more. . Although there is no particular restriction on the preferable upper limit of the refractive index nd, it can be set to 2.5 or less.

The light guide plate has a Young's modulus of 100 GPa or more. By having a Young's modulus of 100 GPa or more, it is possible to increase the precision of processing such as the formation of a diffraction grating by lithography technology using a semiconductor device, and it is also possible to suppress deterioration in image quality due to warping or bending of the light guide plate. can. A preferable range of Young's modulus is 105 GPa or more, a more preferable range is 110 GPa or more, an even more preferable range is 115 GPa or more, and an even more preferable range is 120 GPa or more. Although there is no particular restriction on the upper limit of Young's modulus, it can be set to 180 GPa or less.

The glass used for the light guide plate is preferably optically homogeneous optical glass. Further, it is preferable that the glass has high transmittance in the visible range.

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. Furthermore, the external transmittance at a wavelength of 400 nm converted to a plate thickness of 10 mm is preferably 60% or more, more preferably 70% or more.

The composition of the glass is not particularly limited as long as the desired properties are obtained, but from the viewpoint of stably supplying high-quality glass, glass containing B ₂ O ₃ and La ₂ O ₃ as glass components is preferable. .

(Glass substrate for light guide plate)
One form of the present invention is a glass substrate for a light guide plate, which has a disc shape and is made of glass having 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 at the same time. Note that the cut light guide plate can be used as a light guide plate as it is, or it can be used after polishing or adding a function.

An example of a glass substrate for a light guide plate (hereinafter sometimes referred to as a glass wafer) is shown in FIG. 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 inside this circle are virtual lines 2. Further, 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 rectangle inside the rectangle is also a virtual line 2.

Glass wafer 1 has main surfaces 31 and 32. When at least one of the main surfaces 31 and 32 is divided into a plurality of sections by the imaginary line 2, a light guide path (not shown) is provided in each section. By providing such a light guide path, each glass piece 4 can be used as a light guide plate when the glass wafer 1 is cut along an imaginary line 2, as will be explained later.

The glass pieces 41 and 42 can be made by cutting the virtual line 2 of the glass wafer 1 using a cutting machine such as a dicing machine. Note that the glass pieces 41 are the outermost pieces of glass forming the side surface of the glass wafer 1, and the plurality of glass pieces 42 are surrounded by the glass pieces 41, and have a rectangular or square shape in plan view and are close-packed. is in a state of The obtained glass piece 42 can be used as the light guide plate 5. Therefore, in the glass wafer 1, the virtual line 2 becomes the boundary between each light guide plate 5.
As described above, by cutting the boundaries of the glass wafer 1, a large number of light guide plates 5 can be made from one glass wafer 1.

In order to make a large number of glass pieces 41 (light guide plate 5) at once, the glass wafer 1 may be cut or divided so that a large number of glass pieces 41 are formed on the glass wafer 1 having a large diameter. If the glass wafer 1 having the above-mentioned characteristics is used, the warping and bending of the wafer are extremely small, so that a highly accurate diffraction grating can be formed on each light guide plate 5.

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

For example, the 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, The arithmetic mean roughness Ra of the side surface is 100 μm or less. Note that TTV is the difference between the maximum and minimum thicknesses of the substrate.
From one glass wafer 1, 5 to 20 light guide plates 5 can be formed.

Regarding the cut glass pieces 41, when the main surface 31 is viewed in plan, assuming a virtual circle A inscribed in the contour line and a virtual circle B circumscribed in the plan view shape of each glass piece 41, ( (see FIG. 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 disk shape. Alternatively, the disk-shaped glass wafer 1 can be manufactured by shaping molten glass into a cylinder and slicing it.
Yet another manufacturing method involves bonding or gluing columnar glasses with relatively small cross-sectional areas to each other to create a bundle of columnar glass, which is then formed into a cylinder and then cut to create a disk-shaped glass. Wafer 1 can be manufactured. In the case of such a manufacturing method, the wire 2 is a wire that joins the glasses together.

(display)
Below, one embodiment of the present invention is a display including the above light guide plate. The display of the present invention is not particularly limited as long as it includes the light guide plate of the present invention. A specific example of the display is a head-mounted display that is worn on the human head.

In a head mounted display, the light guide plate of the present invention is placed in front of the right eye and the left eye. The light emitted from the signal processing device and display unit placed inside or outside the head-mounted display is refracted inside the light guide plate, and images are formed on the wearer's right and left retinas. Transmit light.

The air-equivalent optical path length of light traveling through the light guide plate becomes shorter as the refractive index is higher. Therefore, by using the optical glass according to this embodiment having a higher refractive index, the apparent viewing angle can be increased. Furthermore, although the refractive index is high, the specific gravity is kept low, so it is possible to provide a display that is lightweight yet provides the above effects. Furthermore, if the Young's modulus is high and warpage and deflection are extremely small, accurate optical information can be transmitted.

Note that the light guide plate, which is one embodiment of the present invention, can be used for a see-through transmission type head-mounted display, a non-transmission type head-mounted display, and the like.

Glass raw materials were prepared so as to obtain a glass having the composition and optical properties listed in Table 1, and the mixed raw materials were heated, melted, homogenized, clarified, cast into a mold, formed into a sheet glass, and slowly cooled. . No crystal precipitation or striae was observed in any of the plate glasses, and they were optically homogeneous.

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

The degree of coloration λ70 and λ5 were measured by the following method.

Each of the above glasses was processed to have a thickness of 10 mm, parallel to each other and optically polished planes, and the spectral transmittance in the wavelength range from 280 nm to 700 nm was measured. The spectral transmittance B/A was calculated by setting the intensity of the light beam perpendicularly incident on one optically polished plane as intensity A, and the intensity of the light beam emerging from the other plane as intensity B. 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 also includes reflection loss of light rays on the glass surface.

Young's modulus was measured using an ultrasonic method, and specific gravity was measured using an Archimedes method.

The internal transmittance at a wavelength of 400 nm when converted to a thickness of 10 mm is a value excluding reflection loss of light rays on the glass surface.

Next, the sheet glass was machined to produce a number of glass wafers each having a thickness of 0.5 mm and a diameter of 300 mm.

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 1 μm or less.

Next, using semiconductor manufacturing equipment, a glass wafer is coated and a diffraction grating is formed at the light emission position to create a light guide plate. After that, each light guide plate is separated using a dicing machine to create multiple pieces. A light guide plate was obtained.

These light guide plates were incorporated into a head-mounted display to display images. The display has a wide viewing angle and provides high image quality.

(Comparative example)
A light guide plate having a diffraction grating was manufactured using glass having a Young's modulus of 90 GPa, and was incorporated into a head-mounted display to display images. The Young's modulus was low, making it impossible to form a highly accurate diffraction grating, and the light guide plate was slightly deformed by the force applied when incorporating it into a display, resulting in a decrease in image quality.

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 large viewing angle and can easily obtain high image quality.

Claims (4)

A glass substrate for a light guide plate made of glass having a disc shape, a refractive index nd of 1.90 or more, and a Young's modulus of 100 GPa or more. The glass substrate for a light guide plate according to claim 1, wherein the main surface is divided into a plurality of sections, and each section is provided with a light guide path. A light guide plate made of glass having a refractive index nd of 1.90 or more and a Young's modulus of 100 GPa or more. A display comprising the light guide plate according to claim 3.