KR20080043905A - Back light unit for display panel - Google Patents

Abstract

A back light unit for a display panel is provided to equip many laser diode chips and LED(Light Emitting Diode)s and to equip a diffuser or a holographic diffuser between the laser diode and a light guide panel, thereby enhancing the brightness of the illumination light and performing the uniform illumination. A light source(100) includes at least one LED and generates two or more laser beams. A reflection pattern is formed to the inside of a light guide panel(300) so that the light beam generated from the laser light source is diffused or scattered. The laser light source is located at a side of the light guide panel and performs the side surface light emission so that the light source is converted into the surface light source. The light source includes a laser diode for emitting red and blue light beams and an LED for emitting the green light beam. A sheet type holography diffuser is equipped between the laser diode and the diode of the light guide panel.

Description

Backlight unit for display panel {BACK LIGHT UNIT FOR DISPLAY PANEL}

1 is a view showing a schematic diagram of a configuration of a conventional LCD backlight unit;

Figure 2 is a graph showing the radiation angle form of the LED in a general backlight unit,

3 is a schematic view of a backlight unit according to the present invention;

4 is a view illustrating a schematic view of a backlight unit having light sources on both sides as another embodiment according to the present invention;

5 is a diagram illustrating a schematic view of a backlight unit having a lower surface of a light guide plate as another embodiment of the present invention;

6 is a graph illustrating a radiation angle of a laser diode as a light source of the present invention;

7 is a cross-sectional view of a laser diode used in the backlight unit according to the present invention.

The present invention relates to a backlight unit for a display panel, and more particularly, to a display unit backlight unit capable of high system configuration efficiency, excellent color reproducibility, and uniform illumination.

Typically, a liquid crystal display (hereinafter referred to as "LCD") is a plurality of liquid crystal cells arranged in a matrix form and a plurality of control switches for switching the video signal to be supplied to each of these liquid crystal cells The amount of light transmitted from the backlight unit is adjusted by the configured liquid crystal panel to display a desired image on the screen.

Referring to Fig. 1, a configuration of a backlight unit for an LCD of the prior art is shown. The backlight unit for LCD illustrated in FIG. 1 converts a light source 1 for generating light, a lamp housing 3 installed in a form surrounding the light source 1, and light incident from the light source 1 into a planar light source. The light guide plate 5, a reflector 7 positioned below the light guide plate 5 to reflect the light traveling toward the lower surface and the side surface of the light guide plate 5 toward the upper surface, and diffuse the light through the light guide plate 5. Light passing through the first diffusion sheet 9, the first and second prism sheets 11 and 13 for adjusting the traveling direction of the light passing through the first diffusion sheet 9, and the second prism sheet 13 And a second diffusion sheet 15 for diffusing.

A cold cathode fluorescent lamp is mainly used as the light source 1, and the light generated by the light source 1 is incident on the light guide plate 5 through an incident surface existing on the side of the light guide plate 5. The lamp housing 3 has a reflecting surface on its inner surface to reflect light from the light source 1 toward the incident surface of the light guide plate 5.

The light guide plate 5 has an inclined back surface and a horizontal exit surface, and is made such that the incident surface and the exit surface are at right angles. The rear side of the light guide plate 5 is provided so that the reflecting plate 7 faces. The reflector 7 serves to reduce light loss by reflecting light incident to itself through the back of the light guide plate 5 toward the light guide plate 5.

In the above-described LCD backlight unit, when light enters the light guide plate 5 from the light source 1, it is reflected at a predetermined inclination angle from the rear surface which is an inclined surface and proceeds uniformly toward the exit surface. At this time, the light propagated to the lower surface and the side surface of the light guide plate 5 is reflected by the reflector 7 and proceeds toward the exit surface. The light emitted through the exit surface of the light guide plate 5 is uniformly diffused to the entire area by the first diffusion sheet 9.

On the other hand, when the light incident on the liquid crystal panel 17 is vertical, the light efficiency is increased. To this end, it is preferable to stack two first and second prism sheets 11 and 13 so that the traveling angle of the light emitted from the light guide plate 5 is perpendicular to the liquid crystal panel 17. The first and second prism sheets 11 and 13 are formed in the form of a plurality of triangular bars having hills and valleys. In addition, the first and second prism sheets 11 and 13 are arranged such that the prism arrangement directions are perpendicular to each other. The first and second prism sheets 11 and 13 change a propagation path of light so that light incident from the light guide plate 5 is incident perpendicularly to the upper liquid crystal panel 17. The second diffusion sheet 15 secondaryly diffuses the light via the first and second prism sheets 11 and 13.

The liquid crystal panel 17 implements an image by selectively transmitting or blocking light diffused from the second diffusion sheet 15. More specifically, the image is displayed by driving the liquid crystal by the voltage difference between the common electrode (not shown) formed in the upper substrate (not shown) of the liquid crystal panel 17 and the pixel electrode of the lower substrate (not shown). do.

As described above, the LCD backlight unit according to the prior art includes a light source for generating light, a light guide plate for converting the generated light into a planar light source, a reflector for reflecting light traveling toward the lower surface and the side of the light guide plate toward the upper surface, A first diffusion sheet for diffusing light through the light guide plate, first and second prism sheets for adjusting the traveling direction of light, and a second diffusion sheet for diffusing light through the second prism sheet, The generated light is uniformly incident on the liquid crystal panel. In addition, the backlight unit uniformly injects light onto the front surface of the liquid crystal panel, and the liquid crystal panel implements an image by selectively transmitting or blocking light.

2 is a graph showing the radiation angle of the LED used as the light source in the conventional backlight unit. FIG. 2 (a) shows the radiation angle of the direct back light, and FIG. 2 (b) shows the radiation angle when it is illuminated from the side of the light guide plate. As shown in the graph shown in Figure 2 as a light source of the backlight unit, it can be seen that the emission angle of the LED reaches about 80 °.

As described above, the light source of the conventional backlight unit has been used as an LED or a lamp, but in the case of the lamp or the LED, the radiation angle is too high, so that the system configuration efficiency is considerably lowered. There is also a problem of poor color reproducibility due to low color coordinates.

An object of the present invention for solving the above problems is to provide a backlight unit with high system configuration efficiency and color reproducibility, and to enable a compact system implementation. In addition, it is possible to increase the luminance of the illumination light and to enable uniform illumination.

In order to solve the above problems, the present invention is a light source for generating at least one LED and at least two laser light; And a light guide plate having a reflection pattern formed therein so as to diffuse or scatter light generated by the laser light source, wherein the laser light source is positioned on at least one side of the light guide plate and is converted into a surface light source through side light emission. It is characterized by a structure.

The light source may include a laser diode for generating red (R) and blue (B) light and an LED for generating green (G) light, and the light source may have a red laser diode and a green LED on the side of the light guide plate. And at least one blue laser diode as a set.

In addition, the light source is preferably located on one side of the light guide plate, the thickness of the light guide plate becomes smaller as the distance away from the light source, the lower surface of the light guide plate may be inclined, the light source of the light guide plate Located on both sides, it may be formed of a flat plate of the same thickness, it is also preferred that a sheet-shaped holographic diffuser is provided between the side of the laser diode and the light guide plate.

In addition, a second aspect of the present invention is a liquid crystal display device including the above-described backlight unit.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a schematic view of a backlight unit according to the present invention.

As shown in FIG. 3, the backlight unit according to the present invention includes a light source 100 including a laser diode and an LED generating laser light, a light guide plate 300 incident from the light source 100, and converting into a planar light source, A reflecting plate 307 disposed under the light guide plate 300 to reflect light traveling toward the bottom and side surfaces of the light guide plate 300 toward the top surface, and a first diffusion sheet 310 for diffusing light through the light guide plate 300. And first and second prism sheets 320 and 330 for adjusting a traveling direction of light via the first diffusion sheet 310 and a second diffusion sheet for diffusing light through the second prism sheet 330. 340 is provided.

The light guide plate 300 has an inclined rear surface and an exit surface that is horizontal, and is manufactured such that the entrance surface and the exit surface are at right angles. The rear side of the light guide plate 300 is provided so that the reflecting plate 307 faces. The reflector 307 serves to reduce light loss by reflecting light incident to itself through the rear surface of the light guide plate 300 toward the light guide plate 300.

When light is incident on the light guide plate 300 from the light source 100, the light is reflected at a predetermined inclination angle from the rear surface, which is an inclined surface, to uniformly move toward the exit surface. At this time, the light traveling to the lower surface and the side surface of the light guide plate 300 is reflected by the reflecting plate 307 and proceeds toward the exit surface. The light emitted through the exit surface of the light guide plate 300 is uniformly diffused to the entire area by the first diffusion sheet 310.

On the other hand, when the light incident on the liquid crystal panel 400 is perpendicular to the light efficiency is increased. To this end, it is preferable to stack two first and second prism sheets 320 and 330 such that the traveling angle of the light emitted from the light guide plate 300 is perpendicular to the liquid crystal panel 400. The first and second prism sheets 320 and 330 are formed in the form of a plurality of triangular bars having a hill and a valley.

In addition, the first and second prism sheets 320 and 330 are arranged such that the prism arrangement directions are perpendicular to each other. The first and second prism sheets 320 and 330 change a traveling path of light such that light incident from the light guide plate 300 is incident perpendicularly to the upper liquid crystal panel 400. The second diffusion sheet 350 secondaryly diffuses light via the first and second prism sheets 320 and 330.

The liquid crystal panel 400 implements an image by selectively transmitting or blocking light diffused from the second diffusion sheet 340. More specifically, an image is displayed by driving a liquid crystal by a voltage difference between a common electrode (not shown) formed in an upper substrate (not shown) of the liquid crystal panel 400 and a pixel electrode of a lower substrate (not shown). .

As such, in the present invention, by using a light source in combination with an LED or a laser light source instead of one kind, red (R), green (G), and blue to make a white light source while utilizing the excellent color reproduction and system efficiency of the laser diode. (B) A light source capable of implementing light can be compactly implemented.

6 is a graph illustrating a radiation angle of a general laser diode. As shown in FIG. 6, the laser diode has a radiation angle of 8 ° to 20 ° after the cap package as a light emitting device of the light source 100 of FIG. 3. Its high efficiency and excellent color coordinates make it possible to achieve a color reproduction range that is about 20% higher than systems using LEDs.

As illustrated in FIG. 3, the light source is located on the side of the light guide plate by placing a red (R), blue (B) laser diode and a green (G) LED, whereby red (R) and green ( By scattering and diffusing light of G) and blue (B), it serves as a surface light source of backlight illumination.

The light emitted from the laser diode has a much narrower emission angle than the LED, resulting in better system construction efficiency and excellent color reproduction. However, there is a limit that a green laser diode chip such as the size of red and blue laser diodes cannot be implemented to date, and by replacing the green light source with an LED, it is possible to realize three colors by increasing the system configuration efficiency.

As such, when the light source is composed of a combination of a laser diode and an LED, the LED replaces a disadvantage that it is difficult to construct a green laser light from the laser diode into a small diode chip, thereby providing a compact unit by increasing the system configuration efficiency. In addition, it is possible to provide a high quality backlight unit having high color reproducibility.

7 is a cross-sectional view of a laser diode used in the backlight unit according to the present invention. As shown in FIG. 3, the red (R) and blue (B) laser diodes are disposed on the side of the light guide plate to serve as a light source of the backlight unit according to the present invention.

The laser diode is provided with a lower distributed Bragg reflector 121. The lower dispersion Bragg reflector 121 is formed by repeatedly stacking two material layers 121a and 121b having different refractive indices. The n-contact layer 122 is formed on the lower distributed Bragg reflector 121.

On the n-contact layer 122 is a resonator layer consisting of an n-bottom carrier limiting layer 123, an active layer 124, and a p-top carrier limiting layer 125. The current limiting layer 126 is formed on the predetermined region of the resonator layer to restrict the inflow of the current for laser oscillation, and the insulating layer 126a is formed on the remaining region.

The current for laser oscillation flows into the active layer 124 only through the current limiting layer 126. The p-contact layer 127 is formed on the current limiting layer 126 and the insulating layer 126a. An upper distributed Bragg reflector 128 is formed on a predetermined region of the p-contact layer 127.

The upper distributed Bragg reflector 128 is formed by repeatedly stacking two material layers 128a and 128b having different refractive indices, similar to the lower distributed Bragg reflector 121. The lower electrode 130 and the upper electrode 129 are formed on the edge of the n-contact layer 122 and on the edge of the p-contact layer 127, respectively.

In this case, the laser diode supplies current to the resonator layer through the upper electrode 129 and the lower electrode 130, and emits light while the carrier is recombined in the active layer 124. Light emitted from the active layer 124 by carrier recombination increases in intensity while reciprocating between the lower and upper dispersed Bragg reflector layers 121, 128.

Such a laser diode has a narrower wavelength range compared to the wavelength ranges of red (R), green (G), and blue (B) of the conventional light emitting diodes and CCFLs, and emits light in a normal direction with respect to the laminated surface. Release. Therefore, the color reproducibility of the liquid crystal display is improved by using the laser diode.

In addition, the laser diode may emit red and blue light depending on the thickness of the thin film constituting the layer and the thickness of the thin film. Therefore, a color filter (not shown) can be omitted by forming a laser diode emitting red light to correspond to a red pixel and each laser diode emitting blue light to correspond to a blue pixel.

4 is a schematic view of a backlight unit having light sources on both sides of the light guide plate according to another embodiment of the present invention. As shown in FIG. 4, light sources 100 are attached to both sides of the light guide plate 300 for converting light into a surface light source. The light sources include red (R) and blue (B) laser diodes and green (G). ) Is composed of LED. In order to realize various colors and white light of the light source, light sources of red (R), green (G), and blue (B) may be formed on both sides of the light guide plate to increase the luminance of the illumination light of the display panel.

It is desirable to have a light source on the long side of the rectangular panel. This is because by providing light on the long side, it is possible to increase the amount of light as a whole to increase the brightness. Of course, both long and short sides can be considered in consideration of system needs and power demands.

5 is a diagram illustrating a schematic view of a backlight unit having a lower surface of the light guide plate as another embodiment of the present invention. As shown in FIG. 5, the red (R) and blue (B) laser diodes and the green (G) LEDs are located on one side of the light guide plate 300, and the light guide plate moves away from the light source 100. The lower surface of the light guide plate 300 is inclined to decrease the thickness. The shape of the light guide plate 300 may allow the light emitted from the light source 100 to be reflected and scattered on the reflective pattern and the reflective surface formed on the lower surface and directed upward, and the illumination light may be uniformly illuminated as a whole. .

3 to 5, the light emitted from the red (R) and blue (B) laser diode light source 100 is uniformly distributed throughout the light guide plate 300 because of high linearity. Since purging may be difficult to diffuse, it is also preferable to provide a diffuser such as a diffuser or a holographic diffuser between the laser diode and the side of the light guide plate to diffuse the light in advance to allow light to enter the side of the light guide plate to enable uniform illumination. (Not shown)

Holographic diffusers are often used to make beams uniform, but they can also be used to create the shape of the desired beam, and with a designed holographic sheet, a thin thickness (~ 1mm) takes up almost no space. It is possible to effectively control the light without doing so.

In addition, since the holographic diffuser is designed by adjusting the radiation angle at a desired angle in advance, the holographic diffuser can be easily designed according to the system, thereby increasing system efficiency.

Of course, in addition to the holographic diffuser, it is also possible to use optical diffusers such as conventional diffusers or micro lens arrays (MLAs). Using such an optical element, the laser beam may be increased before the laser light is incident on the side of the light guide plate to increase or decrease the uniformity of illumination light by diffusing or scattering the light in the light guide plate.

Here, the micro lens refers to a micro lens having a size of several millimeters or less, and such micro lenses are microlens arrays (MLA) in which one or two dimensions are arranged in one or two dimensions. And a lenticular lens disposed in plural.

The microlenses are used to enhance the sensitivity of one-dimensional image sensors used in a solid-state image pickup device such as a laser disk, a compact disk, a magneto-optical disk, etc. It is used as a condensing means or imaging means for condensing incident light in a photoelectric conversion region, an imaging means for forming an image to be recognized by a liquid crystal printer or an LED printer on a photosensitive member, a filter for processing optical information, and the like. As described above, the microlenses are used in combination with various optical elements or optical components in optical devices.

Diffuser is a material placed in front of a light source to diffuse light and to obtain a smooth image. Real glass, netting, silk, mesh, gelatin, frosted glass, etc. are mainly used, and it is effectively used for specific parts as well as softening of the whole screen. In other words, it refers to an optical element that diffuses light by scattering a beam having a predetermined angle or various wavelengths.

The holographic diffuser may be a plate-shaped individual element, but may be a sheet that can be used by being attached to a light source or a side surface of the light guide plate. By using the sheet-in holographic diffuser in this way, the system configuration efficiency can be further increased, and the production thereof can be made easier.

In the present invention as described above has been described by the specific embodiments, such as specific components and limited embodiments and drawings, but this is provided to help a more general understanding of the present invention, the present invention is not limited to the above embodiments. For those skilled in the art, various modifications and variations are possible from these descriptions.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and all the things that are equivalent to or equivalent to the claims as well as the following claims will belong to the scope of the present invention. .

As such, when the backlight unit according to the present invention is provided, not only the backlight unit having high system configuration efficiency and color reproducibility can be provided, but also a compact size system can be realized.

In addition, by providing a large number of laser diode chips and LEDs with a high system configuration efficiency, it is possible to increase the brightness of the illumination light and to provide uniform illumination by providing a diffuser or a holographic diffuser between the laser diode and the light guide plate.

Claims (7)

A light source for generating at least one LED and at least two laser lights; It includes a light guide plate formed with a reflection pattern therein to diffuse or scatter the light generated from the laser light source, The laser light source is located on at least one side of the light guide plate, the backlight unit for a display panel, characterized in that the structure to switch to a surface light source through the side light emission. The method of claim 1, The light source includes a laser diode for generating red (R) and blue (B) light and a LED for generating green (G) light. The method of claim 2, And at least one light source having at least one red laser diode, a green LED, and a blue laser diode on a side of the light guide plate. The method according to claim 1 or 2, The light source is disposed on one side of the light guide plate, and the thickness of the light guide plate is smaller as the distance away from the light source, the lower surface of the light guide plate, characterized in that the back panel unit. The method according to claim 1 or 2, The light source is positioned on both sides of the light guide plate, the backlight unit for a display panel, characterized in that formed in the same thickness flat. The method of claim 2, And a sheet type holographic diffuser is provided between the laser diode and the side surface of the light guide plate. A liquid crystal display device comprising the backlight unit of claim 1.

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