JP3530291B2 - Planar light emitting device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar light emitting device using unpolarized light as a light source. 2. Description of the Related Art Liquid crystal display devices are used for displays such as personal computers and word processors. In this type of device, the light emitted from the backlight is diffused and diffused by a light diffusion sheet or prism sheet.
By condensing, the screen is designed to be very bright and easy to see for a viewer. However, in practice, light is absorbed when passing through a light guide plate or a liquid crystal cell, so that there is a large difference between the light of the backlight and the light seen through the screen. In particular, when passing through the light guide plate, only one of P-polarized light and S-polarized light is transmitted, and the other is absorbed, so that 50% or more of the light is lost. Therefore, conventionally, a device for reducing the absorption by the light guide plate has been devised. For example, Japanese Patent Application Laid-Open No. 7-64085 discloses that at least one dielectric interference film is laminated on an uneven surface of a prism array, and an interface between the prism array and the dielectric interference film or the laminated dielectric interference film is formed. At the interface between the films, S-polarized light and P-polarized light are separated, one polarized light is transmitted, and the other polarized light is repeatedly subjected to total reflection. A light diffusing sheet or a light diffusing sheet is disclosed, in which light applied to dot printing is diffused, and polarized light is converted to non-polarized light and reused. In this technique, although the separation of the S-polarized light and the P-polarized light is not perfect, it is devised so that one of the polarized lights is emitted more, thereby increasing the amount of light passing through the light guide plate. I have. As another example, Japanese Patent Application Laid-Open No. 6-27420
In the publication, incident light is separated into S-polarized light and P-polarized light by a polarizing beam splitter, and S-polarized light is converted into P-polarized light by passing through a half-wave plate, and then combined with original P-polarized light by a condenser lens. A technique of making a concave mirror enter a liquid crystal cell has been disclosed. As described above, these techniques have a configuration in which, when light emitted from a backlight passes through a light guide plate, only one of P-polarized light and S-polarized light is transmitted and the other polarized light is absorbed. It was done. Therefore, it is assumed that the light incident on the light guide plate is previously unified into P-polarized light or S-polarized light, or that most of the light is incident on the light guide plate as one polarized light, thereby achieving higher luminance and lower power consumption. Has become. In the former prior art, it is premised that the light incident on the prism array is perpendicularly incident on the prism array. The efficiency of the obtained light is low because it is diffused light. Further, the separation of P-polarized light or S-polarized light at the interface depends on the refractive index difference of the medium, but only a few percent of S-polarized light is removed and reused. Therefore, utilization of light is not sufficient. In the latter prior art, P-polarized light or S-polarized light can be separated, and S-polarized light can be converted to P-polarized light and synthesized with the original P-polarized light, but between the concave mirror and the condenser lens, between the concave mirror and the liquid crystal. The need for a distance between the cells hinders downsizing of the apparatus, and also requires expensive optical components such as a polarizing beam splitter and a condenser lens, thereby increasing the cost. Furthermore, in these prior arts, when the peaks and valleys due to the unevenness of the light diffusing sheet are observed from the top, they appear linear, but the lines and the pixel pitch of the liquid crystal cause an interference phenomenon called moiré, which causes There is also a problem such that when viewing the display, the user feels poor image quality. The present invention has been made in view of the above points, and has as its object to provide a planar light emitting device having high luminance, excellent image quality, and a simple structure. In order to achieve the above object, a planar light emitting device according to the present invention comprises two media having different refractive indices adjacent to each other and one end face of which is incident. One of the surfaces orthogonal to the incident surface is an emission surface, and the light incident from the incident surface is converted into first and second polarized lights whose polarization planes are orthogonal to each other. A light guide plate that separates and emits the first polarized light from the emission surface and advances the second polarized light toward the end surface opposite to the incident surface, and is disposed near the incident surface of the light guide plate. A linear light source and a first light source disposed near the end face of the light guide plate on the opposite side to the incident surface for rotating the polarization plane of the second polarized light by 90 degrees.
A 波長 wavelength plate, and the light guide plate disposed outside of the 波長 wavelength plate and reflecting the second polarized light passing through the 波長 wavelength plate through the 波長 wavelength plate. A planar light-emitting device comprising: a first reflector for allowing the second polarized light to enter the first light-emitting device; and a second reflector disposed near a surface of the light guide plate opposite to the light exit surface. The light guide plate is characterized in that one of the media is formed of a thin-film chip, and the chip is uniformly dispersed in the other medium while being inclined with respect to the traveling direction of the incident light. Can be The chips are preferably arranged at an inclination angle of 30 ° to 60 ° with respect to the traveling direction of the incident light, and most preferably 45 °. Thus, the inclination angle is 3
The reason for setting the angle to 0 ° to 60 ° is that the light from a linear light source such as a fluorescent tube, which is a light source, has a spread, and the angle for reflecting only S-polarized light out of the natural polarized light, that is, Brewster This is because the angle to be an angle is not fixed to one. However, considering that the angle at which the light from the light source is most incident on the light guide plate is a direction perpendicular to the incident surface, in order to emit the light in a direction perpendicular to the exit surface,
It is most preferable to set the inclination angle to 45 °. In the thin-film chip, an optimum interface distribution is formed at various points in the light guide plate. Therefore, polarization separation is optimally performed. This is because the angle at which the light from the linear light source is most frequently incident on the light guide plate is a direction perpendicular to the incident surface, and this light is incident on the chip, and the other is approximately the Brewster angle. At the interface with the medium, light that is almost only S-polarized light is emitted perpendicular to the emission surface, the remaining S-polarized light and P-polarized light are transmitted, and at the next interface, part of the S-polarized light is emitted again perpendicular to the emission surface. .
This is repeated, and when the light reaches the end face on the opposite side to the incident surface, only P-polarized light is obtained. Next, the P-polarized light passes through the quarter-wave plate, and the P-polarized light reflected by the first reflection plate again becomes 1
By passing through a quarter-wave plate, the P-polarized light is converted to S-polarized light. A part of the S-polarized light similarly exits perpendicularly to the exit surface, and finally, light with substantially uniform polarization is emitted in the exit direction. Further, since the light guide plate has no unevenness and is uniform, it does not cause moire and does not impair the sense of image quality. Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view schematically showing a configuration example of a planar light emitting device suitable for use in the embodiment. FIGS. 2A and 2B are schematic views showing the light guide plate 10 constituting the configuration of the planar light emitting device, wherein FIG. 2A is a perspective view, FIG. 2B is a side view, and FIG. In this example, the light guide plate 10 is made of an acrylic resin and has two media 3 having different refractive indexes.
And one medium is a thin film chip 8 (refractive index =
1.53), and the chip 8 is uniformly dispersed in the other medium 3 (refractive index = 1.49) in a state of being inclined by 45 ° with respect to the traveling direction of the incident light. The medium 3 is cured by irradiation with visible light. Now, one end face 10a of the light guide plate 10
On the side, a fluorescent tube 1 is provided as a linear light source, and this fluorescent tube 1 is covered with a lamp reflector 2. Also,
On the other end face 10 b side of the light guide plate 10, a reflection mirror 6 is disposed, and this reflection mirror 6 and the other end face 10
A quarter-wave plate 5 is provided between the first and second b. Also,
Near the back surface 10c of the light guide plate 10, a lower surface mirror 7 is provided.
Reflection mirrors are also provided on the remaining two side end surfaces (not shown). Further, as described above, in the configuration of the light guide plate 10, when the medium 8 is arranged at an inclination angle of 45 °, if the light from the fluorescent tube 1 is in a direction perpendicular to the incident surface, the light will be reduced to one. In addition to being incident on the light guide plate 10, light can be emitted in the vertical direction of the display. Thus, since the light from the fluorescent tube 1 is light having a spread, there is no problem due to the fact that the angle as the Brewster angle is not fixed to one. The operation of the planar light emitting device having the above configuration will be described with reference to FIG. First, as shown in FIG. 3A, natural polarized light from the fluorescent tube 1 is perpendicularly incident on an end face 10a of the light guide plate 10 which is a light incident surface. This light is chip 8
And is reflected and transmitted at the interface with the medium 3. Here, the reflectance is about several percent of the whole. If this is the Brewster angle φ shown in the equation (1), only the S-polarized light is reflected. This Brewster angle φ depends on the refractive index of the medium,
This angle reflects only S-polarized light. In the equation (1), n _A and n _B are the refractive indexes of the media A and B, respectively. [Equation 1] Next, the transmitted light is still naturally polarized light including both S-polarized light and P-polarized light. At the next interface between the medium 8 and the medium 3, only the S-polarized light is separated by several percent again. By repeating this, the S-polarized light is emitted in a direction perpendicular to the emission surface. On the other hand, the transmitted light sequentially reduces the S-polarized light at the interface between the medium 8 and the medium 3, so that only the P-polarized light finally remains. Then, as shown in FIG.
The polarized light is transmitted through the quarter-wave plate 5 and then reflected by the reflection mirror 6, and the reflected light is transmitted through the quarter-wave plate 5 again. As a result, the P-polarized light is equivalent to having passed through the half-wave plate, and this P-polarized light is converted into S-polarized light. The light thus converted into S-polarized light is incident on the light guide plate 10 again. Then, as shown in FIG.
Light of only polarization is reflected by several percent, and the reflected light is reflected by the lower mirror 6 and then emitted from the emission surface. In this way, light with almost uniform deflection is finally emitted from the emission surface, and uniformity of the emission distribution in the surface is realized. Moreover, in the embodiment of the present invention, it is not necessary to use expensive optical components such as a beam splitter and a condenser lens as in the related art. In addition, there is no occurrence of an interference phenomenon, which is a cause of poor image quality as in the related art, and therefore, the image quality is not impaired. EXAMPLES Two examples and two comparative examples are described below, and the evaluation methods and evaluation results are shown. Example 1 [1] Preparation of Curing Dispersion First, an acrylic resin of a visible light curable type (refractive index n = 1.49) was prepared as a medium A, and an acrylic resin was used as a medium B. Resin (refractive index n = 1.53) is used for the resin having a diameter of 1.
A disk-shaped one having a thickness of 5 mm and a thickness of 0.2 mm was prepared. Next, 60 g of the medium B is added to 40 g of the medium A.
Was added thereto, and the mixture was stirred and left standing until bubbles were removed to obtain a dispersion for curing. [2] Preparation of Light Guide Plate Light curing tank 30 shown in FIG. 4 having a rectangular parallelepiped resin filling hole 33 having a length of 15 cm, a width of 22 cm and a thickness of 3 mm.
After disposing a triangular prism-shaped member 32 made of an acrylic resin to be an end portion of the light guide plate, a hardening dispersion prepared in advance is injected from the inlet 31 to fill the holes 33, and the dispersion during the dispersion is performed. The medium B is appropriately vibrated at 45 degrees with respect to the light traveling direction of the light guide plate, that is, the triangular prism member 32 arranged at the bottom of the light curing tank is settled and arranged so that the disc surface faces the upper surface of the triangular prism member 32 and is left standing. did. Next, a triangular prism-shaped member (not shown) made of an acrylic resin, which is the other end of the light guide plate, is placed on the top of the filled dispersion for curing, and then a 50 mW light source using a xenon lamp as a light source. After curing for 30 minutes to cure the dispersion for curing, the light curing tank was separated and opened, and the completed light guide plate was taken out. Example 1 is an apparatus using this light guide plate.
It is. (Example 2) After disposing a triangular prism-shaped member 42 made of an acrylic resin to be an end portion of a light guide plate in the light curing tank 40 shown in FIG. 5, a previously prepared dispersion for curing is poured. The medium B being dispersed is filled at 45 degrees with respect to the light traveling direction of the light guide plate, that is, the medium B being dispersed is filled into the hole 43 through the inlet 41, that is, the disk surface is placed on the upper surface of the triangular prism member 32 disposed at the bottom of the light curing tank. The mixture was vibrated appropriately so as to be settled and settled, and allowed to stand. Next, a triangular prism-shaped member (not shown) made of an acrylic resin, which is the other end of the light guide plate, is disposed above the filled hardening dispersion liquid. 50m with xenon lamp as light source
After irradiation with W for 30 minutes to cure the dispersion for curing, the light curing tank was separated and opened, and the completed light guide plate was taken out.
Example 2 is an apparatus using this light guide plate. (Comparative Example 1) A light diffusion sheet (bead coating type) and a prism sheet having an apex angle of about 90 ° are used as a conventional backlight having a dot print pattern, a diffuse reflection sheet, a fluorescent tube, a reflector, and an acrylic light guide. Comparative Example 2 is an apparatus in which two sheets are arranged orthogonally. Comparative Example 2 Comparative Example 3 uses the polarizing element described in JP-A-7-64085. Each of the planar light emitting devices of the above two examples and two comparative examples is evaluated by the following evaluation method. (1) The brightness of the light transmitted through the light guide plate at the center of the screen is measured and evaluated. (2) Measure the amount of light transmitted through the light guide plate and evaluate how much light has passed before and after the light guide plate. (3) Five types of liquid crystal cells are combined with the device of each example, and at the time of lighting, the image quality (confirmation of occurrence of interference fringes) is evaluated by human eyes. If at least one of the combinations has a poor image quality, it is considered unsuitable for this evaluation item. Table 1 shows the evaluation results. [Table 1] As is apparent from the results, in the example of the present invention, both the luminance and the amount of transmitted light were larger than those of the comparative example, and the image quality was also good. As described above, in the planar light emitting device of the present invention, one medium constituting the light guide plate is a thin film chip, and this chip is inclined with respect to the traveling direction of the incident light. In this state, the structure is uniformly dispersed in the other medium, so that light can be effectively used, and light emission with high luminance and excellent image quality can be realized. In addition, it can be realized with a simple configuration, and can be made compact, and the manufacturing cost can be kept low.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view schematically showing a configuration of a planar light emitting device applied to an embodiment of the present invention. FIG. 2 is a surface applied to the embodiment of the present invention. FIG. 3 is a diagram schematically showing a light guide plate of the planar light emitting device. FIG. 3 is a diagram for explaining the operation of the planar light emitting device applied to the embodiment of the present invention. FIG. FIG. 5 is a view for explaining a method for manufacturing a light guide plate of a planar light emitting device to be applied. FIG. 5 is a view for explaining a method for manufacturing a light guide plate of a planar light emitting device applied to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 Fluorescent tube 5 1/4 wavelength plate 6 Reflector 7 Lower mirror 8 Chip (medium B) 3 Medium (medium A) 10 Light guide plate

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Claims (1)

(57) [Claim 1] Two media having different refractive indices are adjacent to each other, and one end surface is an incident surface,
In addition, one of the surfaces orthogonal to the incident surface is an emission surface, and separates light incident from the incident surface into first and second polarized lights whose polarization planes are orthogonal to each other. A light guide plate that emits polarized light from the emission surface and causes the second polarized light to travel toward the end surface opposite to the incident surface; and a linear light source disposed near the incident surface of the light guide plate. It is arranged near the end face on the opposite side to the incident surface of the light guide plate,
A quarter-wave plate for rotating the polarization plane of the second polarized light by 90 degrees; and a second polarized light disposed outside the quarter-wave plate and reflecting the second polarized light passing through the quarter-wave plate. Thereby, the first reflector for allowing the second polarized light to enter the light guide plate via the quarter-wave plate, and the first reflector disposed near the surface opposite to the emission surface of the light guide plate 2
Reflector, and a planar light-emitting device comprising: a light guide plate, one of the media constituting a thin film chip, the chip is inclined with respect to the traveling direction of the incident light,
A planar light emitting device, wherein the planar light emitting device is uniformly dispersed in another medium.