JP2011238484A - Backlight device and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain in-plane luminance unevenness caused by luminance distribution of a light source in the vicinity of an incident end of the light source when a laser light source as a point light source is adopted as a sidelight type backlight.SOLUTION: A first backlight unit 2 of a liquid crystal display 100 is formed by laminating two sets of plane light sources 200a, 200b including light sources 20a, 20b having red, green, and blue laser light sources, and light guide plates 21a, 21b having light-transmitting sections for generating linear laser light sources from the spot-like laser light sources 20a, 20b and fine optical elements 25a, 25b for irradiating linear laser light as illumination light to a back surface of the liquid crystal display element 1 in a normal-line direction of a display surface of a liquid crystal display element 1, and illumination light having uniform in-plane luminance distribution can be generated by overlapping light emitted from these plane light sources. A liquid crystal display for providing a compact image with high quality can be attained in this simple structure.

Description

  The present invention relates to a backlight device and a liquid crystal display device that illuminate the liquid crystal display device from the back surface of the liquid crystal display device with a plurality of laser light sources and display an image on the liquid crystal display device.

  Since the liquid crystal display element included in the liquid crystal display device does not emit light by itself, it is necessary to provide a backlight device on the back surface of the liquid crystal display element as a light source for illuminating the liquid crystal display device. In recent years, there has been an increasing demand for thinning liquid crystal display devices. A thin light guide plate is provided, a light source is disposed so as to face the side surface, and light is incident on the light guide plate from the side surface. A sidelight system that creates a light source is widely used.

  The liquid crystal display element of the liquid crystal display device includes a color filter, and by transmitting only light of a part of the wavelength through the color filter from the fluorescent lamp that emits white light in a continuous spectrum, red, green, The blue display color is extracted for color expression. In this way, when only a part of the wavelength band of light from the continuous spectrum light source is cut out to obtain the display color, if the color purity of the display color is increased in order to widen the color reproduction range, the transmission wavelength of the color filter The bandwidth must be set narrow. For this reason, when trying to increase the color purity of the display color, there arises a problem that the amount of light transmitted through the color filter is reduced and the luminance is lowered.

  Further, a fluorescent lamp that is generally used has an emission spectrum having a peak at a wavelength shifted to orange of about 615 nm in the red wavelength region due to the characteristics of the phosphor, for example, with respect to red. For this reason, in particular, when trying to increase the color purity in the wavelength region of 630 to 640 nm which is preferable as pure red in red, there is a problem that the amount of transmitted light is extremely reduced and the luminance is remarkably reduced.

In order to solve such problems, in recent years, a monochromatic light emitting diode (hereinafter referred to as LED (Light Emitting Diode)) having a narrow wavelength width, that is, high color purity, and a backlight device using a laser as a light source are provided. Liquid crystal display devices have been proposed. In particular, a laser has a very excellent monochromaticity and high light emission efficiency, and thus provides a high-luminance image with a wide color reproduction range and enables a liquid crystal display device with low power consumption.

  However, when a point light source such as an LED or a laser is used as the light source of a sidelight type backlight device, the luminance near the light source becomes extremely high, and as a result, there is a problem that luminance unevenness occurs near the light incident end. is doing. Such a problem can be remedied by, for example, arranging a large number of point light sources in a line at a narrow interval and approaching a linear light source, but a highly uniform in-plane luminance distribution is required. Since the backlight device of the liquid crystal display device requires a large number of light sources, there are problems in terms of power consumption, assembling property, and cost.

  Therefore, conventionally, a technique for obtaining a surface light source having a uniform in-plane luminance distribution with the smallest possible number of light sources has been reported. For example, in the liquid crystal display device of Patent Document 1, light emitted from a light emitting element can be diffused by a refractive effect by covering the light emitting element with a hemispherical light-transmitting material made of a plurality of materials having different refractive indexes. It is possible to make the light distribution in the light guide plate light incident part closer to a linear light source.

  For example, in the surface light source of Patent Document 2, the light diffusion surface for converting the point light source to the linear light source and the in-plane luminance distribution of the backlight device are made uniform on the light diffusion surface provided on the back surface of the light guide plate. And a light diffusing surface for the purpose. On the light diffusion surface for converting a point light source to a linear light source, the coverage of the diffused material in the portion where the luminance of the point light source is high is lowered, while the coverage of the diffused material in the portion where the luminance of the point light source is low. By making it high, it becomes possible to convert a point light source into a linear light source.

JP 2006-269289 A Japanese Patent No. 2917866

  According to the above technique, by adding an optical element that converts a point light source into a linear light source, light having a substantially uniform luminance distribution in a one-dimensional direction can be incident from the side surface of the light guide plate. Although it is possible to obtain a surface light source with high uniformity of luminance distribution, such an optical element requires a complicated structure. In addition, when a highly directional point light source such as a laser is used as the light source, a more complex optical element with higher diffusibility is required, and the optical distance required to convert from a point light source to a linear light source is large. Since it becomes longer, there is a disadvantage that the apparatus becomes larger. For this reason, it is not optimal when a laser light source is used.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a backlight device and a liquid crystal display device that suppresses uneven luminance with a simple and compact configuration.

  In order to solve the above-described problems and achieve the object, the backlight device of the present invention converts a plurality of light sources that emit light having a divergence angle, and light emitted from the light sources into linear light. A plurality of the light guide plates, comprising: a light propagation portion; and a light guide plate having an optical element portion that emits the linear light as a planar light toward the liquid crystal display element, and transparent to the planar light. Are stacked in the normal direction of the display surface of the liquid crystal display element, the plurality of optical element portions are arranged at positions corresponding to the display surface of the liquid crystal display element, and the light emitted from the plurality of light guide plates is added together And illuminating the liquid crystal display element.

  According to the present invention, there is provided a compact backlight device and a liquid crystal display device that have a simple configuration and suppress uneven luminance even in a backlight device that employs a plurality of light sources that emit light having a divergence angle. Can do.

It is a figure which shows typically the structure of the liquid crystal display device (transmission type liquid crystal display device) of Embodiment 1 which concerns on this invention. (A) (b) is a figure which shows roughly an example of a structure of the planar light source which comprises the backlight unit of Embodiment 1 which concerns on this invention. It is a figure which shows notionally the one-dimensional luminance distribution in the Y-axis direction of the laser light source which propagates the inside of a light-guide plate. It is a graph which shows the calculation result by the simulation of the one-dimensional luminance distribution in the X-axis direction of the illumination light irradiated from a backlight unit. It is a graph which shows the measurement result of the one-dimensional luminance distribution in the X-axis direction of the illumination light irradiated from a backlight unit. It is the figure which showed notionally the optical path of the laser beam in a light propagation part. It is a graph which shows the one-dimensional luminance distribution in the Y-axis direction of the laser beam after light propagation part transmission.

Embodiments of a backlight device and a liquid crystal display device according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment.

Embodiment 1 FIG.
FIG. 1 is a diagram schematically showing a configuration of a liquid crystal display device 100 which is a transmissive display device according to the first embodiment of the present invention. In order to facilitate the description of the drawing, the short side direction of the liquid crystal optical element 1 is the Y-axis direction, the long side direction is the X-axis direction, and the direction perpendicular to the XY plane is the Z-axis direction. The surface 1a side is defined as the + Z-axis direction. Further, the upward direction of the liquid crystal display device 100 is defined as the + Y axis direction, and the light emission direction of the light source 20a described later is defined as the + X axis direction.

  As shown in FIG. 1, the liquid crystal display device 100 includes a transmissive liquid crystal display element 1, a first optical sheet 31, a second optical sheet 32, a backlight unit 2 that is a backlight device, and a light reflecting sheet. 15 and these components 1, 31, 32, 2 and 15 are arranged in the Z-axis direction. The liquid crystal display element 1 has a display surface 1a parallel to an XY plane including an X axis and a Y axis orthogonal to the Z axis. Note that the X axis and the Y axis are orthogonal to each other.

  The liquid crystal display device 100 further includes a liquid crystal display element driving unit (not shown) that drives the liquid crystal display element 1 and a light source driving unit (not shown) that drives the light sources 20 a and 20 b included in the backlight unit 2. The light source 20a includes a plurality of first light sources 60a that emit a red monochromatic light that is a first monochromatic light having a divergence angle, and a green monochromatic light that is a second monochromatic light having a divergence angle. And a plurality of third light sources 62a that emit a blue monochromatic light having a divergence angle and a third monochromatic light. Similarly, the light source 20b includes a plurality of first light sources 60b having a divergence angle and emitting red monochromatic light, a plurality of second light sources 61b having a divergence angle and emitting green monochromatic light, and a divergence. And a plurality of third light sources 62b that emit blue monochromatic light. The operations of the liquid crystal display element driving unit and the light source driving unit are controlled by a control unit (not shown).

  The control unit performs image processing on a video signal supplied from a signal source (not shown) to generate a control signal, and supplies the control signal to the liquid crystal display element driving unit and the light source driving unit. The light source driving unit drives the light sources 20a and 20b in accordance with control signals from the control unit to emit light from the light sources 20a and 20b, respectively.

  The backlight unit 2 converts the emitted lights 22a and 22b including red, green, and blue light emitted from the light sources 20a and 20b into white illumination lights 33a and 33b that are directed in the + Z-axis direction, and is used for the liquid crystal display element 1. The light is emitted toward the back surface 1b. The illumination lights 33 a and 33 b are applied to the back surface 1 b of the liquid crystal display element 1 through the second optical sheet 32 and the first optical sheet 31. Here, the first optical sheet 31 has an action of directing light emitted from the backlight unit 2 in a normal direction with respect to the screen of the liquid crystal display device 100, and the second optical sheet 32. It suppresses optical effects such as fine illumination unevenness.

  A light reflecting sheet 15 is disposed in the −Z-axis direction of the backlight unit 2. The light emitted from the backlight unit 2 to the back side is reflected by the light reflecting sheet 15 and used as illumination light for irradiating the back surface 1 b of the liquid crystal display element 1. As the light reflecting sheet 15, for example, a light reflecting sheet based on a resin such as polyethylene terephthalate or a light reflecting sheet in which a metal is deposited on the surface of the substrate can be used.

  The liquid crystal display element 1 has a liquid crystal layer parallel to an XY plane orthogonal to the Z-axis direction. The display surface 1a of the liquid crystal display element 1 has a rectangular shape, and the X-axis direction and the Y-axis direction shown in FIG. 1 are directions along two mutually orthogonal sides of the display surface 1a. The liquid crystal display element driving unit changes the light transmittance of the liquid crystal layer in units of pixels in accordance with a control signal supplied from the control unit. Each pixel is further composed of three sub-pixels, each of which has a color filter that transmits only red, green, and blue light, and generates a color image by controlling the transmittance of each sub-pixel. To do. Accordingly, the liquid crystal display element 1 can spatially modulate the illumination light incident from the backlight unit 2 to generate image light, and emit the image light from the display surface 1a. According to the first embodiment, for example, unlike the white light by the conventional fluorescent lamp, the light source driving unit is controlled by the control unit, the luminance of the red light emitted from the light sources 20a and 20b, and the green light It is possible to adjust the ratio between the brightness of the light and the brightness of the blue light, and the power consumption can be reduced by adjusting the light quantity of each color according to the ratio of each color brightness required for each video signal It is also possible to do.

  The backlight unit 2 includes a light source 20 a including a laser light source 60 a that emits red light, a laser light source 61 a that emits green light, and a laser light source 62 a that emits blue light, and a display surface 1 a of the liquid crystal display element 1. A first planar light source 200a comprising a light guide plate 21a arranged in parallel to the light source, a laser light source 60b that emits red light, a laser light source 61b that emits green light, and a laser light source 62b that emits blue light. And a second planar light source 200b composed of a light guide plate 21b arranged in parallel to the display surface 1a of the liquid crystal display element 1. 2A is a schematic view of the first planar light source 200a viewed from the + Z-axis direction, and FIG. 2B is a schematic view of the second planar light source 200b viewed from the + Z-axis direction.

  Laser light sources 60a, 61a, and 62a included in the first planar light source 200a are disposed to face a light incident end surface 23a that is one end surface of the light guide plate 21a in the -X-axis direction, and a plurality of red, green, Laser light sources 60a, 61a and 62a having blue laser light emitting elements are arranged at equal intervals in the Y-axis direction. The light guide plate 21a included in the first planar light source 200a is a plate-like member made of a transparent material, and a plurality of micro optical elements 25a are formed on the back surface 24a that is the surface opposite to the liquid crystal display element 1. And an optical element portion 28a. The red, green, and blue light emitted from the laser light sources 60a, 61a, and 62a is incident on the light guide plate 21a from the light incident end surface 23a of the light guide plate 21a, and propagates through the light guide plate 21a while being totally reflected.

  Similarly, in the second planar light source 200b, the laser light sources 60b, 61b, and 62b are disposed to face the light incident end surface 23b that is one end surface in the + X-axis direction of the light guide plate 21b. Laser light sources 60a, 61a, and 62a having red, green, and blue laser light emitting elements are arranged at equal intervals in the Y-axis direction. The light guide plate 21b of the second planar light source 200b is a plate-like member made of a transparent material, and a plurality of micro optical elements 25b are formed on the back surface 24b that is the surface opposite to the liquid crystal display element 1. It has an optical element portion 28b. Red, green, and blue light emitted from the laser light sources 60b, 61b, and 62b is incident on the light guide plate 21b from the light incident end face 23b of the light guide plate 21b, and propagates while totally reflecting the light guide plate 21b.

  The light sources 20a and 20b of the first planar light source 200a and the second planar light source 200b employ laser light emitting elements having the same characteristics, and the laser light sources 60a, 61a and 62a and the laser light source 60b, The same arrangement method is employed, such as the interval between 61b and 62b, the arrangement direction and angle of the light guide plate with respect to the light incident end faces 23a and 23b. The light guide plates 21a and 21b included in the first planar light source 200a and the second planar light source 200b have the same structure. That is, the first planar light source 200a and the second planar light source 200b have the same characteristics.

  The backlight unit 2 has a relationship in which these two planar light sources 200a and 200b having the same characteristics are rotated by 180 degrees with respect to a normal line (Z axis in FIG. 1) with respect to the display surface 1a of the liquid crystal display element 1. The four side end surfaces of the light guide plate 21a and the light guide plate 21b are stacked so as to be aligned on the same plane. In other words, the light source 20a included in the first planar light source 200a and the light source 20b included in the second planar light source 200b are arranged to face each other, and the light source 20a emits light toward the + X axis direction. On the other hand, since the light source 20b emits light toward the −X axis direction, the traveling direction of the light emitted from each light source is opposite. However, the illumination lights 33a and 33b emitted from the planar light sources 200a and 200b are both emitted toward the back surface 1b of the liquid crystal display element 1.

  As described above, the backlight unit 2 according to the first embodiment has a configuration in which the two planar light sources 200a and 200b are stacked in the Z-axis direction. The illumination light emitted from the backlight unit 2 obtained when the light sources 20a and 20b included in the backlight unit 2 are turned on is added to the illumination light 33a and 33b emitted from the two planar light sources 200a and 200b. It is a thing. Accordingly, the in-plane luminance distribution in the XY plane of the illumination light emitted from the first backlight unit 2 is the sum of the in-plane luminance distributions in the XY plane of the two planar light sources 200a and 200b. . The Z-axis direction is the direction of illumination light emitted from the backlight unit 2 toward the liquid crystal display element 1.

  The light guide plates 21a and 21b are plate-like members having a thickness of 2 mm, for example, formed of a transparent member. As shown in FIGS. 1 and 2, the optical element portions 28 a and 28 b have a plurality of hemispherical convex shapes (hereinafter referred to as convex lens shapes) on the back surfaces 24 a and 24 b that are opposite to the liquid crystal display element 1. ) Fine optical elements 25a and 25b. The micro optical elements 25a and 25b are for converting the light propagating through the light guide plates 21a and 21b into light emitted toward the + Z-axis direction that is the direction of the back surface 1b of the liquid crystal display element 1. Therefore, the emitted lights 22a and 22b that have become linear light in the light propagation portions 26a and 26b become planar light in the optical element portions 28a and 28b in which the micro optical elements 25a and 25b are formed, and the liquid crystal display element 1 Is emitted in the direction of.

  The outgoing lights 22a and 22b incident from the light incident end faces 23a and 23b of the light guide plates 21a and 21b are repeatedly reflected in the light guide plates 21a and 21b by total reflection at the interfaces between the light guide plates 21a and 21b and the air layer. Progress in the axial direction. However, when the light enters the optical element portions 28a and 28b on which the micro optical elements 25a and 25b are formed, the light is refracted by the curved surfaces, and the entire surface of the light guide plates 21a and 21b on the liquid crystal display element 1 side and the interface between the air layers. Light that does not satisfy the reflection condition is generated, and the light is emitted from the surface of the light guide plates 21 a and 21 b toward the back surface 1 b of the liquid crystal display element 1.

  The plurality of micro optical elements 25a and 25b formed in the optical element portions 28a and 28b of the light guide plates 21a and 21b are arranged according to the positions in the XY plane on the light guide plates 21a and 21b, that is, the number per unit area, Its size has changed. Thereby, it is possible to control the in-plane luminance distribution of the illumination lights 33a and 33b irradiated from the light guide plates 21a and 21b.

  In the first embodiment, as shown in FIG. 2, the arrangement density of the micro optical elements 25a and 25b with respect to the position in the traveling direction (X-axis direction in FIG. 2) of the emitted lights 22a and 22b, which are laser beams, is set. It has a changing structure. More specifically, the micro optical elements 25a and 25b are not arranged in the vicinity of the light incident end faces 23a and 23b, but are opposed to the light incident end faces 23a and 23b from the position of the center of the light guide plates 21a and 21b in the X-axis direction. It is provided in the area up to the end face on the side to be used. The arrangement density is configured to continuously change from sparse to dense toward the end face direction of the light guide plates 21a and 21b from the vicinity of the center position in the X-axis direction.

  As an example of the shape of the micro optical elements 25a and 25b, for example, a convex lens shape having a curvature of about 0.15 mm, a maximum height of about 0.005 mm, and a refractive index of about 1.49 may be adopted as the surface shape. it can. The light guide plates 21a and 21b and the micro optical elements 25a and 25b can be made of acrylic resin, but are not limited to this material. As long as the material has good light transmittance and excellent moldability, other resin materials such as polycarbonate resin or glass material may be used instead of acrylic resin.

  In the first embodiment, the fine optical elements 25a and 25b are convex lens shapes, but the present invention is not limited to this. As long as it has a structure in which the laser light traveling in the X-axis direction in the light guide plate is refracted in the Z-axis direction and is irradiated toward the back surface 1b of the liquid crystal display element 1, other shapes may be used. Alternatively, a fine optical element composed of a random concavo-convex pattern such as sandblast may be adopted.

  However, in the case of a convex lens shape, it is possible to refract light with a transparent structure, and there is an advantage that manufacture is easy because the shape is simpler than that of a structure such as a prism. Further, even when the light guide plate is enlarged, it can be easily handled because it can be manufactured by printing. In addition, the laser light can be refracted in the Z-axis direction even with a random uneven shape such as by sandblasting, but in the case of a convex lens shape, a convex shape can be designed, so that a uniform luminance distribution as a planar light source can be obtained. There is an advantage that the design is easy.

  In Embodiment 1, the thickness of the light guide plate is 2 mm, but the present invention is not limited to this. In terms of reducing the thickness and weight of the liquid crystal display device and improving the light utilization efficiency by increasing the number of multiple reflections, it is desirable to use a light guide plate with a small thickness. Since the laser light source is a light source having a small light emitting surface area and high directivity, it is possible to obtain high optical coupling efficiency even for a light guide plate having a small thickness. However, at this time, it is also necessary to consider the problem of a decrease in rigidity caused by reducing the thickness of the light guide plate.

  The laser light sources 60a and 60b included in the light sources 20a and 20b have peaks of 640 nm, the laser light sources 61a and 61b have peaks of 532 nm, the laser light sources 62a and 62b have peaks of 460 nm, and have a very monochromatic spectrum with a full width at half maximum of 1 nm. The divergence angle is 40 degrees in full width at half maximum in the fast axis direction and 10 degrees in full width at half maximum in the slow axis direction. In the first embodiment, the laser light emitting element is provided so that the fast axis direction thereof is parallel to the short side direction of the side end surfaces of the light guide plates 21a and 21b. This is because the fast axis direction with a large divergence angle is parallel to the short side direction on the side end surface of the light guide plate, that is, the direction in which the distance between the opposing surfaces of the light guide plate is the smallest (Z-axis direction in FIG. 1). This is because the number of reflections of the laser light within the light guide plate increases, and the amount of light incident on the micro optical elements 25a and 25b provided on the light guide plates 21a and 21b increases. Thereby, it is possible to improve the light extraction efficiency (the amount of light emitted toward the direction of the liquid crystal display element / the amount of light propagating in the light guide plate) by the micro optical elements 25a and 25b.

  According to the first embodiment, the light diameter of the laser light emitted from the light sources 20a and 20b is a point light source that is extremely small relative to the size of the light guide plate incident end faces 23a and 23b in the Y-axis direction. However, it propagates while reflecting a sufficient optical distance in a region that does not have the fine optical elements 25a and 25b that are the light propagation portions 26a and 26b provided in the vicinity of the light incident end faces 23a and 23b of the light guide plates 21a and 21b. be able to. For this reason, it spreads by its own divergence angle, and overlaps with the light of another adjacent laser light emitting element, thereby forming linear white light having a uniform luminance distribution and chromaticity distribution in the Y-axis direction, that is, a linear light source.

  FIG. 3 is a conceptual diagram for explaining that a laser beam emitted from two adjacent laser light sources of the same color propagates a certain optical distance to form a linear light source. For example, in the laser light source 60a, the two adjacent laser light sources of the same color are the two laser light sources 60a sandwiching the laser light sources 61a and 62a one by one. As shown in FIG. 3, the luminance distribution 40 with respect to the Y-axis direction position of the laser light emitted from a single laser light source at an arbitrary position in the X-axis direction is a Gaussian-shaped angular luminance distribution originally possessed by the laser light. As a result, it has a shape in which the central luminance is high and the luminance rapidly decreases as the distance from the center increases. Therefore, when a single laser beam is incident on the fine optical structure, the luminance distribution of the laser beam is reflected in the in-plane luminance distribution of the illumination light emitted from the light guide plate, resulting in luminance unevenness.

  However, it is possible to spatially superimpose a plurality of laser beams emitted from laser light sources arranged close to each other. For example, when a single laser beam having the luminance distribution 40 in FIG. 3 and a single laser beam having the luminance distribution 41 are superimposed, the distributions are averaged, and a uniform luminance distribution such as the luminance distribution 42 is obtained. Thus, a linear light source having a uniform luminance distribution in the light source arrangement direction that is the Y-axis direction can be created. By making the luminance distribution of each color uniform, white light generated by combining red, green, and blue light has a uniform chromaticity distribution in addition to the luminance distribution. Therefore, even if the light has a single non-uniform distribution, the distribution can be averaged by superimposing a plurality of lights. Therefore, the lines with uniform luminance distribution and chromaticity distribution in the light source arrangement direction can be obtained. Can be produced.

  As described above, in order to superimpose the lights of the adjacent laser light emitting elements, the laser needs to propagate through a certain optical distance determined by the divergence angle of the laser and the arrangement interval of the laser light sources. The light guide plates 21a and 21b included in the planar light sources 200a and 200b according to the first embodiment are arranged in the arrangement direction of the laser light emitting elements at a divergent angle of the laser light before the laser light enters the fine optical elements 25a and 25b. The optical propagation distance necessary for sufficient spatial expansion is provided. For this reason, it becomes possible to enter the optical element portions 28a and 28b on which the fine optical elements 25a and 25b are formed after becoming a highly uniform linear light source.

  Further, in the first embodiment, the light sources 20a and 20b have a configuration in which a plurality of laser light emitting elements having equal divergence angles and angular luminance distributions are arranged at equal intervals, and thus a linear laser with higher uniformity of luminance distribution. A light source is obtained.

  As described above, part of the light incident on the optical element portions 28a and 28b as a linear laser light source is refracted by the micro optical elements 25a and 25b on the back surfaces 24a and 24b of the light guide plates 21a and 21b. Irradiation light 33a and 33b is irradiated from the surface of the light guide plates 21a and 21b toward the back surface 1b of the liquid crystal display element 1. At this time, the light incident on the micro optical elements 25a and 25b is a linear light source that is uniform in the laser light source arrangement direction (Y-axis direction). The liquid crystal display element 1 is illuminated as the illumination lights 33a and 33b.

  On the other hand, the planar light sources 200a and 200b are illuminating lights 33a and 33b because of light propagation portions 26a and 26b provided to convert the laser light source into a linear light source in the X-axis direction, which is the light traveling direction. It has a region that does not radiate. However, in the first embodiment, the planar light sources 200a and 200b are stacked and arranged so as to compensate for a region in which each other does not emit illumination light. That is, a region where the planar light source 200a does not emit light and a region where the planar light source 200b emits light, that is, a region on the −X axis direction side from the vicinity of the center of the X axis in FIG. Further, the area where the planar light source 200b does not emit light and the area where the planar laser light source 200a emits light, that is, the area on the + X-axis direction side from the vicinity of the X-axis center in FIG. For this reason, the backlight unit 2 including the planar light source 200a and the planar light source 200b can irradiate illumination light from the entire surface.

  Further, in the first embodiment, the micro optical element 25a that determines each luminance distribution so that the luminance distribution formed by adding the luminance distributions in the X-axis direction of the planar light source 200a and the planar light source 200b becomes uniform. , 25b is optimized for the arrangement density in the X-axis direction.

  FIG. 4 is a graph showing a calculation result by simulation of the one-dimensional luminance distribution in the X-axis direction of the illumination lights 33a and 33b irradiated from the backlight unit 2. Specifically, the one-dimensional luminance distribution 50 in the X-axis direction of the planar light source 200a, the one-dimensional luminance distribution 51 in the X-axis direction of the planar light source 200b, and the X-axis direction of the backlight unit 2 obtained by adding these luminance distributions. It is a graph which shows the calculation result by simulation of the one-dimensional luminance distribution 52 in.

  As is clear from FIG. 4, the one-dimensional luminance distribution 50 of the illumination light 33a emitted from the planar light source 200a is near the center position in the X-axis direction of the light guide plate 21a from the light incident end face 23a side in the -X-axis direction. No light is emitted from to. However, the luminance gradually increases from the vicinity of the center position in the X-axis direction of the light guide plate 21a toward the + X-axis direction, and constant luminance is maintained in the vicinity of the end surface side facing the light incident end surface 23a in the + X-axis direction. On the other hand, the one-dimensional luminance distribution 51 of the illumination light 33b emitted from the planar light source 200b has a luminance distribution that is reverse to that of the planar light source 200a. That is, no light is emitted from the light incident end face 23b side in the + X axis direction to the vicinity of the center position in the X axis direction of the light guide plate 21b. However, the luminance gradually increases from the vicinity of the center position in the X-axis direction of the light guide plate 21b toward the -X-axis direction, and constant luminance is provided in the vicinity of the end surface side facing the light incident end surface 23b in the -X-axis direction. keep.

  The in-plane luminance distribution 52 of the illumination light emitted from the first backlight unit 2 generated by adding the illumination light 33a emitted from the planar light source 200a and the illumination light 33b emitted from the planar light source 200b is: The distribution is uniform in the X-axis direction. FIG. 5 shows the result of actually measuring the in-plane luminance distribution of the illumination light emitted from the prototype backlight unit 2 according to the configuration of the first embodiment. As is clear from FIG. 5, in the first backlight unit 2 in which two planar light sources 200a and 200b are stacked in the Z-axis direction, illumination light having excellent uniformity in the laser beam traveling direction (X-axis direction) is obtained. You can see that The above is the configuration and operation of the backlight unit 2. The configuration and operation of the light guide plates 21a and 21b will be described in more detail.

  The light guide plates 21a and 21b are plate-like members having a thickness of 2 mm, for example, formed of a transparent member such as acrylic resin (PMMA: Poly Methyl Methacrylate). The outgoing lights 22a and 22b, which are laser beams incident from the light incident end faces 23a and 23b of the light guide plates 21a and 21b, are reflected inside the light guide plates 21a and 21b by total reflection at the interface between the light guide plates 21a and 21b and the air layer. The process proceeds in the X-axis direction while repeating the above. The light guide plates 21a and 21b transmit light 22a and 22b emitted from the light sources 20a and 20b in the light guide plates 21a and 21b and propagate through the light propagation portions 26a and 26b, and the light propagation portions 26a and 26b through X. It has optical element portions 28a and 28b formed with fine optical elements 25a and 25b for converting the traveling direction of the outgoing lights 22a and 22b traveling in the axial direction into the Z-axis direction.

  The light propagation portions 26a and 26b of the light guide plates 21a and 21b are provided in the vicinity of the light incident end surfaces 23a and 23b. When the laser beams emitted from the light sources 20a and 20b are incident on the light guide plates 21a and 21b from the light incident end faces 23a and 23b, they first propagate in the X-axis direction through the light propagation portions 26a and 26b. In the light propagation portions 26a and 26b, the front surfaces (surfaces on the liquid crystal display element 1 side) and the back surfaces (surfaces opposite to the liquid crystal display element 1) of the light guide plates 21a and 21b on which the emitted lights 22a and 22b are incident are particularly protrusions and the like. It is a plane without the structure. Accordingly, the outgoing lights 22a and 22b propagating through the light propagation portions 26a and 26b propagate while preserving their divergence angles and traveling directions. The outgoing lights 22a and 22b emitted from the light sources 20a and 20b spread spatially according to their divergence angles by propagating through the light propagation portions 26a and 26b.

  In particular, the light propagation portions 26a and 26b provided in the light guide plates 21a and 21b are for making the one-dimensional luminance distribution in the Y-axis direction, which is formed by adding the laser beams emitted from the adjacent laser light emitting elements 20 and 21, more uniform. The optical propagation portions 26a and 26b require a certain optical distance X in the X-axis direction.

  The micro optical elements 25a and 25b included in the light guide plates 21a and 21b are called hemispherical convex shapes (hereinafter referred to as convex lens shapes) on the back surfaces 24a and 24b (surfaces opposite to the liquid crystal display element 1) of the light guide plates 21a and 21b. ). The convex lens shape converts the emitted lights 22a and 22b propagating in the light guide plates 21a and 21b in the X-axis direction into light emitted in the direction of the back surface 1b (+ Z-axis direction) of the liquid crystal display element 1. The outgoing lights 22a and 22b incident from the light incident end faces 23a and 23b of the light guide plates 21a and 21b propagate through the light propagation portions 26a and 26b and then enter the micro optical elements 25a and 25b with the traveling direction set as the X-axis direction. To do. The outgoing lights 22a and 22b incident on the micro optical elements 25a and 25b are refracted by the curved surface of the convex lens shape, and are subjected to total reflection conditions at the interface between the surfaces of the light guide plates 21a and 21b (the liquid crystal display element 1 side) and the air layer. Light that no longer meets the requirements is generated. Light that does not satisfy the total reflection condition is emitted from the surfaces of the light guide plates 21 a and 21 b toward the back surface 1 b of the liquid crystal display element 1.

  The light emitted from the laser light sources 20a and 20b, which are point light sources, spreads at its own divergence angle by propagating through the light propagation portions 26a and 26b. The light spreading at its own divergence angle is spatially overlapped with other adjacent laser light, and becomes a linear light source having a uniform luminance distribution in the arrangement direction (Y-axis direction) of the laser light emitting elements. This linear light source is incident on the micro optical elements 25a and 25b and becomes uniform illumination lights 33a and 33b emitted toward the back surface 1b of the liquid crystal display element 1.

  Hereinafter, the laser light emitting element 80 included in the laser light source 20a and the laser light emitting element 81 of the same color adjacent to the laser light emitting element 81 in the Y-axis direction will be described as an example, and the light propagation part 26a provided in the light guide plate 21a will be described in detail. Here, the laser light emitting elements 80 and 81 include two adjacent laser light sources of the same color (for example, a green laser light source 61a and a blue laser light source 62a) among the red, green, and blue laser light sources included in the light source 20a. One of the adjacent laser light sources 60a).

  FIG. 6 is a diagram conceptually showing the optical paths of the laser beams 80p and 81p emitted from the laser light emitting elements 80 and 81 and entering the light guide plate 21a from the light incident end face 23a. FIG. 7 shows linear light sources generated by adding the one-dimensional luminance distributions 80q and 81q in the Y-axis direction of the laser beams 80p and 81p propagated through the light propagation part 26a with the optical distance in the X-axis direction being X. Is a graph showing a one-dimensional luminance distribution 82q.

  As shown in FIG. 6, the laser light emitting elements 80 and 81 are adjacent to each other at a distance d between the respective light emitting points in the Y-axis direction, and are respectively disposed to face the light incident end face 23a of the light guide plate 21a. The distance between the light emitting surfaces of the laser light emitting elements 80 and 81 and the light incident end face 23a is set to a distance f. The laser light-emitting elements 80 and 81 have the same characteristics, and the angular luminance distribution of a substantially Gaussian shape having a half-value half-angle α in the XY plane of the laser beams 80p and 81p emitted from them has the same shape. is doing.

  Laser beams 80p and 81p emitted from the laser light emitting elements 80 and 81 are incident on the light guide plate 21a from the light incident end face 23a and propagate through the light propagation portion 26a. At this time, the optical distance X in the X-axis direction of the light propagation part 26a is defined by Expression (1). Here, d is the distance between the light emitting points of the laser light emitting elements 80 and 81, f is the distance between the emission surface of the laser light emitting elements 80 and 81 and the light incident end face 23a, and α is the light emitted from the laser light emitting elements 80 and 81. Is a half-value half-angle of the divergence angle in the XY plane, and β is a half-value half-angle of the divergence angle in the XY plane of the laser beams 80p and 81p propagating in the light guide plate 21a.

  However, the half value half angle β in the light guide plate 21a is defined by the equation (2). Here, the refractive index of the layer propagating before the laser beams 80p and 81p emitted from the laser light emitting elements 80 and 81 enter the light guide plate 21a is n1, and the refractive index of the light guide plate 21a is n2.

  Here, since the light emitting areas of the laser light emitting elements 80 and 81 are sufficiently small with respect to the distance d between the light emitting points of the laser light emitting elements 80 and 81, the size thereof is ignored.

  In the above formulas (1) and (2), the intersection of the laser beam 80p and the laser beam 81p at the position where the luminance distribution in the Y-axis direction has half the peak luminance existing on each optical axis. The optical distance X necessary for holding the image is determined.

  Since the laser beam 80p and the laser beam 81p have the same angular luminance distribution and have an angular luminance distribution that is symmetric with respect to their optical axes, they propagate through the optical distance X defined by the equations (1) and (2). As shown in FIG. 7, the laser beams 80p and 81p have a luminance L / 2 at an intermediate point (Y = y2) between points (Y = y0, y1) each having a peak luminance L. The luminance of the intermediate point (Y = y2) becomes L by the overlap of these laser beams 80p and 81p. Conventionally, since there is a dark part that is a dark part between bright parts that are bright parts existing on the optical axes of the laser beams 80p and 81p, luminance unevenness occurs in the Y-axis direction. . However, by providing the optical distance X defined by the equations (1) and (2), the bright portion (Y = y0, y1) between the bright portions (Y = y0, y1) by the laser beams 80p and 81p has the same brightness. = Y2) can be interpolated. At the same time, since the luminance distribution between these bright portions (Y = y0, y1) is averaged, a linear light source having high uniformity can be generated.

  As described above, the laser beams 80p and 81p propagate through the light propagation part 26a having the optical distance X defined by the expressions (1) and (2), thereby minimizing the size of the light propagation part 26a. It is possible to generate a linear light source having a uniform luminance distribution in the Y-axis direction while suppressing the number of the light sources.

  The micro optical element 25a is provided in a region from the end in the + X-axis direction of the light propagation part 26a to the end in the + X-axis direction of the light guide plate 21a, and the arrangement density is sparsely and densely continuous in the + X-axis direction. It is formed so as to change. The structure and characteristics of the micro optical element 25a are as described above.

  The emitted light 22a emitted from the laser light source 20a and propagated through the light propagation part 26a having the optical length X in the X-axis direction is a linear light source that is uniform in the arrangement direction of the laser light sources in the Y-axis direction. Thereafter, the liquid crystal display element 1 is incident on the optical element portion 28a and becomes a surface light source having a uniform in-plane luminance distribution to illuminate the liquid crystal display element 1.

  Although the light guide plate 21a is described here, the light guide plate 21b similarly includes a light propagation portion 26b that satisfies the expressions (1) and (2), and becomes a linear light source having high uniformity, and the micro optical element 25b. Is incident on the optical element portion 28b, and illuminates the liquid crystal display element 1 as a surface light source having a uniform in-plane luminance distribution.

  The backlight unit 2 composed of the light guide plate 21a and the light guide plate 21b serves as a planar light source having a high uniformity of in-plane distribution, and the illumination light does not have uneven luminance distribution, and therefore has high image quality without uneven display. The liquid crystal display device 100 can be provided.

  As described above, a planar light source having high uniformity is generated by setting the length in the X-axis direction of the light propagation portions 26a and 26b to the optical distance X defined by the expressions (1) and (2). It is possible. Note that the uniformity of the luminance distribution can be further improved by setting the optical distance to be longer than X defined by the equations (1) and (2). The above is a specific example of the configuration and operation related to the light guide plates 21a and 21b.

  In the first embodiment, the light propagation portions 26a and 26b of an area necessary for converting a laser light source as a point light source into a linear laser light source are provided in the effective image display area. Accordingly, it is not necessary to provide a light propagation part around the planar light source part while securing a sufficient optical distance for the laser light to propagate, and therefore the image display plane (XY plane) of the liquid crystal display device 100. It is possible to reduce the ratio of the area of the backlight device 2 to that area. That is, it is possible to realize the liquid crystal display device 100 in which the bezel that is the cabinet portion surrounding the image display portion is thin while providing an image with good image quality. Moreover, since the light propagation part is designed with the thickness of the light guide plate, the liquid crystal display device 100 can be thinned.

  As described above, according to the liquid crystal display device 100 of the first embodiment, it is necessary to form a linear laser light source that spatially overlaps with other laser light that is closer to the divergence angle of the laser light. Since it is possible to provide a sufficient optical distance, which is a long propagation distance, it is possible to generate illumination light having a uniform in-plane luminance distribution. Therefore, a liquid crystal display that can display a good image without uneven brightness even when a point light source and a highly directional laser light source are used as a sidelight light source, which has been a problem with uneven brightness in the conventional surface. An apparatus can be provided.

  Further, in the first embodiment, the above configuration effectively utilizes the effective image display area of the liquid crystal display device, and the backlight device is enlarged with respect to the simple configuration and the effective image display area of the liquid crystal display device. It is possible to realize without.

  In the first embodiment, since the light propagation portions 26a and 26b and the optical element portions 28a and 28b are provided in the same light guide plate, the light propagation portions 26a and 26b and the optical element portions 28a and 28b are individually provided. Compared with a system using light guide plates and combining them, there is less light loss due to coupling of the light guide plates and the like, and the light utilization efficiency is improved, the number of parts is reduced, and the assemblability is improved.

  In Embodiment 1, laser light sources are employed as the light sources 20a and 20b of the backlight unit 2, but the present invention is not limited to this. The present invention is also effective for other light sources having a small light emitting area and a divergence angle, such as a laser light source, and by applying to such a light source, high in-plane luminance distribution uniformity as with a laser light source. It is possible to create a planar light source having For example, a high effect can be obtained by applying to an LED light source.

  As in the liquid crystal display device 100 of the first embodiment, by adopting a laser having excellent monochromaticity as the light sources 20a and 20b of the backlight unit 2, the color purity of the display color can be increased, and it has been widely used in the past. As a result, a liquid crystal display device 100 capable of expressing colors more vividly than when a fluorescent lamp or LED is used is obtained.

  In the first embodiment, the light source 20a, 20b of the backlight unit 2 has a red laser light source 60a having a peak wavelength at 640 nm, a green laser light source 61a having a peak wavelength at 532 nm, and a peak wavelength at 460 nm. Although the blue laser light source 62a is employed, the present invention is not limited to this, and a laser that emits visible monochromatic light having different wavelengths may be employed. In addition, for example, it is effective to employ an LED that emits monochromatic light having relatively excellent monochromaticity as the light source of the backlight unit 2, but in order to obtain a wider color reproduction region, the wavelength width is as short as possible. In other words, it is desirable to employ a laser light source having excellent monochromaticity because the effect of widening the color reproduction region is high. In the first embodiment, it is desirable to select the monochromatic light source employed as the light source of the backlight unit 2 so as to be a combination constituting white light.

  In a conventional liquid crystal display device, a fluorescent lamp or LED is used as a light source. When the transmission wavelength of a color filter included in the liquid crystal display element 1 is set narrow to increase color purity, light loss due to the color filter is caused. It increases and the brightness of the image decreases. On the other hand, in the first embodiment, since the color purity is improved by increasing the monochromaticity of the light source, the light loss is reduced, the decrease in brightness is suppressed, and the color purity can be increased with low power consumption.

  In addition, the laser light source is superior to the monochromatic LED light source in that it is excellent in monochromaticity, can be driven with low power consumption, and further has the advantage of improving the coupling efficiency to the light guide plate due to its high directivity. Have

  The backlight unit 2 in which a plurality of planar light sources 200a and 200b are stacked in the first embodiment is provided on the light guide plate 21a provided on the upper layer (side closer to the liquid crystal display element 1) or on the light guide plate 21a. Each of the micro optical elements 25a is made of a transparent member. That is, the light guide plate 21a is light irradiated from the light guide plate 21b disposed below (the side closer to the light reflection sheet 15), and is transparent to light incident from the back surface of the light guide plate 21a, and the light loss. And high light utilization efficiency can be obtained.

  In the first embodiment, the plurality of planar light sources included in the backlight unit 2 have the same characteristics, but the present invention is not limited to this. As described above, the first embodiment has a configuration in which the backlight unit 2 having a uniform in-plane luminance distribution is generated by adding the illumination light emitted from a plurality of planar light sources in the XY plane direction. One of the elements of the invention. As long as this is achieved, the in-plane luminance distribution of illumination light emitted from a plurality of planar laser light sources may be different.

  In the first embodiment, two sets of planar light sources each including a laser light source are stacked. However, the present invention is not limited to this. For the same reason as above, any number of sets are stacked as long as the illumination light that uniformly illuminates the entire liquid crystal display element is generated by adding the illumination light emitted by each planar light source in the XY plane. It is good also as a structure.

  As described above, the illumination light emitted from a plurality of planar light sources is added in the XY plane direction to generate a backlight unit with a uniform in-plane luminance distribution. Whatever the in-plane luminance distribution is, any number of sets may be stacked. However, in this case, the light guide plate included in each planar light source is provided with a light propagation portion that does not have a fine optical element in the vicinity of the light incident end of the laser light source. This light propagation part is necessary for the light emitted from the laser light emitting element to overlap spatially with the light emitted from the other adjacent laser light emitting elements and to make the luminance distribution in the array direction of the laser light emitting elements uniform. Has an optical distance. For this reason, the laser light incident on the fine optical element is always a linear light source. Thereby, the illumination light which is refracted by the fine optical element and is irradiated from the front surface of the light guide plate toward the back surface 1b of the liquid crystal display element 1 does not have uneven luminance distribution. Accordingly, it is possible to provide a high-quality liquid crystal display device 100 with no display unevenness.

  If the above configuration is satisfied, there are no restrictions on the laser light source arrangement method, such as the arrangement interval and the arrangement direction and angle with respect to the incident end face of the light guide plate. Moreover, it is good also as a structure which arrange | positions a laser light source facing either end surface of the light-guide plate 4 sides. At this time, by making the incident end face of the laser light source the end face on the short side of the liquid crystal display device, the optical propagation distance of the laser light can be effectively increased, so that the in-plane luminance distribution is more uniform. It becomes possible to obtain excellent illumination light.

  In addition, according to the first embodiment, a laser light source propagates a sufficiently long optical distance in a light guide plate while performing multiple reflections, and a plurality of laser light sources are used in a spatially overlapping manner. Therefore, an effect that speckle noise which is a problem in an image display apparatus using a high laser light source is reduced can be obtained.

  As described above, the present invention is useful for a backlight device and a liquid crystal display device having a uniform in-plane luminance distribution, and realizes a high-quality and compact liquid crystal display device.

  DESCRIPTION OF SYMBOLS 1 Liquid crystal display element, 2 Backlight unit, 200a, 200b Planar light source, 20a, 20b Light source, 21a, 21b Light guide plate, 25a, 25b Fine optical element, 31, 32 Optical sheet, 15 Light reflection sheet.

Claims (11)

A plurality of light sources that emit light having a divergence angle;
A light propagation part that converts light emitted from the light source into linear light, and an optical element part that emits the linear light as planar light toward the liquid crystal display element. A light guide plate that is transparent,
A plurality of the light guide plates are stacked in a normal direction of the display surface of the liquid crystal display element, and the plurality of optical element portions are arranged at positions corresponding to the display surfaces of the liquid crystal display elements and emitted from the plurality of light guide plates. A backlight device that illuminates the liquid crystal display element by adding light.   The light source includes a plurality of first light sources that emit first monochromatic light, a plurality of second light sources that emit second monochromatic light, and a plurality of third light sources that emit third monochromatic light. 2. The backlight device according to claim 1, wherein the light propagation unit converts light emitted from the first light source, the second light source, and the third light source into linear white light. .   3. The backlight device according to claim 1, wherein the light propagation unit has an optical distance in which light emitted from a plurality of light sources spreads by its divergence angle and spatially overlaps with each other. 4. The optical distance X of the light propagation part is defined as n1 as the refractive index of the layer that propagates before the light emitted from the light source enters the light guide plate, n2 as the refractive index of the light guide plate, and the distance between the light emitting points of the adjacent light sources. D, the distance between the light emitting surface of the light source and the light incident end surface of the light guide plate is f, the half-value half angle of the divergence angle of the light emitted from the light source in a plane parallel to the display surface of the liquid crystal display element is α, The half-value half angle β of the divergence angle in the plane parallel to the display surface of the liquid crystal display element in the first light guide plate of the emitted light is expressed by the following equation:

When expressed by

4. The backlight device according to claim 1, wherein the backlight device is expressed by:   The backlight device according to claim 4, wherein the light source emits light of the same color.   The optical element portion is formed from the vicinity of the region where the light from the first light source, the second light source, and the third light source becomes linear white light to the end surface facing the light incident end of the light guide plate. The backlight device according to any one of claims 2 to 5, wherein:   The backlight device according to claim 1, wherein the optical element portion has a plurality of hemispherical convex portions formed on a surface opposite to the liquid crystal display element.   8. The backlight device according to claim 1, wherein a light incident end surface of the light guide plate is a side surface parallel to a short side direction of the liquid crystal display element. 9.   9. The backlight device according to claim 2, wherein the first light source, the second light source, and the third light source are laser light sources that emit visible monochromatic light.   The backlight device according to claim 9, wherein the first light source, the second light source, and the third light source are laser light sources that emit red, green, or blue monochromatic light, respectively.   A liquid crystal display device comprising the backlight device according to claim 1.

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