JP5929601B2 - Surface light source device and liquid crystal display device - Google Patents

Description

  The present invention relates to a liquid crystal display device using a laser light source as a backlight.

  The liquid crystal display element included in the liquid crystal display device does not emit light by itself. For this reason, the liquid crystal display device includes a backlight as a surface light source on the back surface of the liquid crystal display element as a light source for illuminating the liquid crystal display element. Conventionally, a cold cathode fluorescent lamp (hereinafter referred to as CCFL (Cold Cathode Fluorescent)), which is a discharge tube in which a phosphor is coated on the inner wall of a glass tube, has been the mainstream as a light source for the back line. However, in recent years, the demand for backlights using LEDs as light sources has been rapidly increasing as the performance of light-emitting diodes (hereinafter referred to as LEDs (Light Emitting Diodes)) has dramatically improved.

  However, in CCFLs and LEDs, the wavelength of emitted light is continuously distributed over a wide wavelength range, so in a liquid crystal display device having a backlight using these light sources, the color purity of the display color This is a problem that it is difficult to increase the color reproduction range and the color reproduction range is narrow.

  In recent years, for the purpose of providing a liquid crystal display device having a wide color reproduction range, it has been proposed to use a laser light source that emits light only at a single wavelength (very narrow wavelength range) as the light source of the backlight. Yes. Since single-wavelength light emitted from a laser light source has extremely high color purity, a liquid crystal display device equipped with a backlight using this laser light source can display a wide color reproduction range and realizes a vivid image display It becomes possible to do.

  However, when a laser light source is employed, since light emitted from the laser light source has high directivity, it is difficult to obtain a backlight that illuminates the entire screen of the liquid crystal display element with high uniformity.

  A liquid crystal display device using a conventional laser light source as a backlight has an optical system composed of a light guide plate and a plurality of lenses. In this conventional liquid crystal display device, the light emitted from the laser light source is shaped into a light intensity distribution of a desired shape via the optical system, and is emitted as planar light with high uniformity.

JP 2008-066612 (page 4, FIG. 1)

  However, a conventional liquid crystal display device requires a plurality of optical elements and a spatial propagation distance in order to shape a highly directional light intensity distribution emitted from a laser light source into a planar uniform light intensity distribution. Further, since these optical elements and a backlight having a spatial propagation distance are provided on the back side of the liquid crystal display element, the liquid crystal display device becomes larger and complicated, leading to an increase in price. In recent years, liquid crystal display devices are required to be reduced in size and price, but it has been difficult to reduce the size and price of liquid crystal display devices with the configuration of a conventional liquid crystal display device.

  An object of the present invention is to provide a liquid crystal display device using a laser light source as a backlight light source and capable of highly uniform display with a simple configuration.

Surface light source device according to the present invention includes a housing that having a diffuse reflecting surface on the inner side, a plurality of laser light sources for emitting a laser beam inside said housing, said housing from said laser light is emitted A reflective polarizing plate that is disposed at a position and transmits only light polarized in one direction and reflects light polarized in a direction orthogonal to the one direction, the polarization direction of light that can be transmitted by the reflective polarizing plate, characterized in that the polarization direction of the laser beam emitted from the laser light source are perpendicular to each other.

  The present invention can provide a liquid crystal display device having a high uniformity with a small and simple configuration in a liquid crystal display device using a laser light source as a backlight light source.

1 is a schematic configuration diagram of a liquid crystal display device according to a first embodiment of the present invention. It is a schematic block diagram of the liquid crystal display device of Embodiment 2 of this invention.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view schematically showing a configuration of a liquid crystal display device according to Embodiment 1 for carrying out the present invention. As shown in FIG. 1, the liquid crystal display device according to the present embodiment includes a liquid crystal panel 6 and a backlight 10 that illuminates the liquid crystal panel 6. The backlight 10 includes a plurality of laser light sources 1, a laser beam emitted from the laser light source 1, a backlight housing 2 having a diffuse reflection surface on the inner surface, and a light emitting surface of the backlight housing 2. At least one diffuser plate 3 disposed, at least one prism sheet 4 disposed on the exit surface side of the diffuser plate 3, and only light polarized in one direction disposed on the exit surface side of the prism sheet 4 The reflection polarizing plate 5 reflects light that is transmitted and polarized in a direction orthogonal to the one direction. The backlight housing 2 is made of, for example, a box-shaped aluminum having a hollow inside, and the light emission surface is made of an opening. The inner surface other than the opening is a diffuse reflection surface. This diffuse reflection surface can be realized, for example, by attaching a diffuse reflection sheet made of polyester. The laser light source 1 has a property of emitting polarized light. Further, in the present embodiment, the laser light source 1 is arranged so that the emission surface of the laser light source is exposed on the side surface of the backlight housing 2 with respect to the light emission surface.

  In FIG. 1, a transmission axis direction that is a polarization direction of light that can be transmitted through the reflective polarizing plate 5 is defined as a y-axis, which is a direction perpendicular to the paper surface. Further, the direction perpendicular to the y axis and parallel to the exit surface of the reflective polarizer 5 is defined as the x axis, and the direction perpendicular to the x axis and the y axis and perpendicular to the exit surface of the reflective polarizer 5 is defined as z. Define as an axis.

  In the present embodiment, the polarization direction of the laser beam immediately after being emitted from the laser light source 1 is configured to be orthogonal to the y-axis direction that is the transmission axis direction of the reflective polarizing plate 5. That is, the polarization direction of the laser light immediately after being emitted from the laser light source 1 is a direction parallel to the xz plane (a direction parallel to the paper surface in FIG. 1).

  In the liquid crystal display device configured as described above, the laser light having polarization characteristics in a direction parallel to the xz plane and emitted into the backlight housing 2 is transmitted through the diffusion plate 3 and the prism sheet 4, The reflection polarizing plate 5 is reached. Here, since the reflective polarizing plate 5 is set so that the polarization direction of light that can be transmitted is in the y-axis direction (perpendicular to the paper surface of FIG. 1), the laser light that has reached the reflective polarizing plate 5 Some of the components that have been converted from the direction parallel to the plane of the drawing to the direction perpendicular to the plane of the figure due to the birefringence characteristics of the diffusion plate 3 and the prism sheet 4 in the optical path, etc. Except for this, most of the component has a polarization direction immediately after emission from the laser light source (a direction parallel to the paper surface of FIG. 1), and is reflected by the reflective polarizing plate 5 and returned to the backlight housing 2.

  The laser light returned into the backlight housing 2 is repeatedly diffused and reflected in the region surrounded by the backlight housing 2 and the reflective polarizing plate 5, and the directivity is gradually disturbed. It propagates through the backlight housing 2 as diffused light that fills the region surrounded by the body 2 and the reflective polarizing plate 5. As described above, the laser light propagating through the region surrounded by the backlight housing 2 and the reflective polarizing plate 5 while repeatedly diffusing and reflecting is diffusely reflected on the inner surface of the diffusion plate 3, the prism sheet 4, and the backlight housing 2. The polarization direction is disturbed by repeating transmission and reflection on the surface, etc., and the polarization direction is gradually changed from a direction parallel to the paper surface of the figure to a direction perpendicular to the figure, and passes through the reflective polarizing plate 5 to illuminate the liquid crystal panel To come.

  In this way, since the polarization direction of the laser light immediately after being emitted from the laser light source 1 is orthogonal to the transmission axis direction of the reflective polarizing plate 5, the laser immediately after being emitted from the laser light source 1. The light cannot pass through the reflective polarizing plate 5 and most of the light is reflected by the reflective polarizing plate 5, but the reflected laser light is surrounded by the backlight housing 2 and the reflective polarizing plate 5. While repeatedly diffusing and reflecting in the region, the polarization direction is gradually disturbed, transmitted through the reflective polarizing plate 5, and emitted from the backlight 10 toward the liquid crystal panel 6. As a result, when the liquid crystal panel 6 is illuminated by repeating the diffusion and reflection and finally changing the polarization direction of most of the laser light emitted in the backlight housing 2 and passing through the reflective polarizing plate 5, The directivity of the laser light is random, and the in-plane distribution of the light intensity is uniform.

  In the present embodiment, the configuration is such that the polarization direction of the laser light immediately after being emitted from the laser light source 1 is orthogonal to the transmission axis direction of the reflective polarizing plate 5. Since the laser light is emitted from the backlight 10 to the liquid crystal panel 6 side, the multiple reflection and refraction are sufficiently repeated in the region surrounded by the backlight housing 2 and the reflective polarizing plate 5. The light emitted from the light has a uniform spatial intensity distribution, and becomes light that uniformly illuminates the entire surface of the liquid crystal panel 6.

  As described above, in the liquid crystal display device according to the present embodiment, the laser light immediately after being emitted from the laser light source 1 is light on a beam having high directivity, but is emitted from the backlight 10 toward the liquid crystal panel 6. In this case, the entire surface of the liquid crystal panel 6 can be illuminated uniformly. As a result, in a liquid crystal display device using a laser light source as a backlight light source, a liquid crystal display device capable of uniform screen display with a simple configuration can be provided.

  In this embodiment, the laser light source is disposed on the side surface of the backlight housing with respect to the light emitting surface. However, the laser light source is disposed at a position where the laser light emitted from the laser light is inside the backlight housing. As long as it is emitted, the backlight housing is not limited to the side surface. In FIG. 1, the direction of the laser light emitted from the laser light source is directed to the emission surface side of the backlight housing, but is not limited thereto.

Embodiment 2. FIG.
FIG. 2 is a cross-sectional view schematically showing a configuration of a liquid crystal display device according to Embodiment 2 for carrying out the present invention. The configuration of the liquid crystal display device in the present embodiment is substantially the same as the configuration of the liquid crystal display device described in the first embodiment, but includes a diffusion lens in the vicinity of the position of the laser light source and the exit surface of the laser light source. The point is different.

  In the present embodiment, as in the first embodiment, the polarization direction of the laser light immediately after being emitted from the laser light source 1 is orthogonal to the y-axis direction that is the transmission axis direction of the reflective polarizing plate 5. It is configured to do.

  In FIG. 2, a plurality of laser light sources 1 are arranged at a substantially equal pitch on a surface (bottom surface) facing the light emitting surface of the backlight housing 2, and are adjacent to each emitting surface of the laser light source 1. A diffusing lens 7 is installed to widen the divergence angle of the laser light emitted from.

  The effect of the liquid crystal display device thus configured will be described. In the first embodiment, the effect of diffusing the directivity of the laser light emitted from the laser light source is the scattering effect by the diffuse reflection surface of the diffuser plate, the prism sheet, and the inner surface of the backlight casing, which are constituent elements of the backlight. Rely only on. In particular, immediately after the laser light is emitted from the laser light source and before reaching the diffuse reflection surface of the diffuser plate or the backlight casing, it propagates a considerable distance with high orientation. In the optical path, the effect that laser light is converted into diffused light, that is, the effect of improving the uniformity of illumination cannot be obtained. As a result, in order to make the spatial intensity distribution of the light emitted from the backlight uniform, it is necessary to sufficiently perform scattering by the diffuser reflection surface of the diffuser plate, the prism sheet, and the backlight housing inner surface, Depending on conditions such as the number of individual laser light sources, it is necessary to ensure a sufficiently long distance from the diffuse reflection surface on the inner surface of the backlight housing to the reflective polarizing plate.

  In the present embodiment, the laser light source 1 is arranged at a substantially equal pitch on the bottom surface of the backlight housing 2, and the divergence angle of the laser light is converted into a wide divergence angle immediately after being emitted from the laser light source 1 by the diffusion lens 7. doing. With this configuration, since the laser light is diffused immediately after being emitted from the laser light source 1, the distance from the diffuse reflection surface on the inner surface of the backlight housing 2 to the reflective polarizing plate 5 can be further shortened. Further, the liquid crystal display device can be further reduced in size and thickness.

  As described above, in the liquid crystal display device according to the present embodiment, since the laser light immediately after being emitted from the laser light source can be converted into diffused light, the liquid crystal display device using the laser light source as the backlight light source has a simple configuration. Thus, a liquid crystal display device that can display a uniform screen and can be made smaller or thinner can be provided.

DESCRIPTION OF SYMBOLS 1 Laser light source, 2 Backlight housing | casing, 3 Diffusing plate, 4 Prism sheet 5 Reflective polarizing plate, 6 Liquid crystal panel, 7 Diffusing lens, 10 Backlight

Claims (3)

A housing that having a diffuse reflecting surface on the inner side,
A plurality of laser light sources emitting laser light into the housing ;
A reflective polarizing plate that is disposed at a position where the laser light is emitted from the housing , reflects only light polarized in one direction and reflects light polarized in a direction orthogonal to the one direction ;
With
A surface light source device, wherein a polarization direction of light that can be transmitted through the reflective polarizing plate and a polarization direction of laser light emitted from the laser light source are orthogonal to each other. Wherein disposed in proximity to the exit surface of the laser light source, surface light source device of claim 1, further comprising a diffusion lens to expand the divergence angle of the laser beam. LCD panel,
The surface light source device according to claim 1 or 2, wherein the liquid crystal panel is irradiated with light.
A liquid crystal display device comprising:

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