JP2008066162A - Surface light source and liquid crystal display device - Google Patents

Abstract

A surface light source for a liquid crystal backlight having a uniform brightness with a laser is realized.
The surface light source of the present invention is provided with an illumination optical system including at least one laser, a light guide plate, and at least two lenses, so that the polarization of the laser is maintained and light is transmitted by a liquid crystal panel. It can be used effectively and a bright surface light source can be realized.
Light beams from a plurality of lasers are configured to enter the rod lens incident end face.
With this configuration, a plurality of lasers can be used, and the brightness can be improved. Moreover, a surface light source can be made into a color by making a several laser into the laser of another wavelength of RGB.
[Selection] Figure 1

Description

  The present invention relates to a surface light source that illuminates a liquid crystal panel from its back surface and a liquid crystal display device including the surface light source.

  Thin and light liquid crystal display devices capable of displaying images have rapidly spread due to price reduction and development of high image quality technology due to progress in manufacturing technology, and are widely used in monitors for personal computers and TV receivers.

  A transmissive liquid crystal display device is generally used as the liquid crystal display device. The transmissive liquid crystal display device includes a planar light source called a backlight, and forms an image by spatially modulating illumination light from the light source using a liquid crystal panel.

  As the backlight, a backlight that uses a cold cathode tube, which is a substantially linear light source, and is incident from the side surface of a thin light guide plate is often used. The basic configuration is shown in FIG. FIG. 5A is a top view of a backlight using a conventional cold cathode ray tube observed from the emission surface side, and FIG. 5B is a cross-sectional view. In FIG. 5A, a reflector 130 described later is omitted.

  Light emitted from the cold cathode ray tube 120 and incident from the incident surface 111 on the side surface of the light guide plate 110 propagates while repeating total reflection between the opposing main surfaces. A part of the propagating light is emitted by forming a diffuse reflection layer or reflection unevenness having a specific density distribution and size on the surface of the reflection surface 113 which is the opposite surface of the emission surface 112. By appropriately setting the density distribution, the size distribution, etc. that form the diffuse reflection layer or the reflection unevenness, it is possible to perform almost uniform illumination over the entire surface of the liquid crystal panel. By providing the reflection sheet 140 on the reflection surface 113 side of the light guide plate 110, a part of light leaking from the reflection surface to the outside of the light guide plate is reflected to the light guide plate side to prevent light loss. In addition, in order to illuminate a liquid crystal panel (not shown) with desired light distribution characteristics by controlling the directivity of light emitted from the backlight, a diffusion film, a prism sheet, or the like is provided on the light exit surface 112 side of the light guide plate 110. The optical film 150 is generally installed.

  At this time, a reflector 130 surrounding the cold cathode ray tube 120 and opening toward the incident surface 111 of the light guide plate 110 is provided. As a result, the light emitted from the cold cathode ray tube can be guided to the light guide plate without any excess.

  More recently, light emitting diodes (hereinafter referred to as LEDs) with high luminous efficiency have been developed, and it has been proposed to use them as light sources for liquid crystal backlights.

  As a method for obtaining planar light emission that can be used as a backlight from an LED that is a point light source, a method in which a large number of LEDs are arranged on an end surface of a light guide plate and light is directly input is generally used. An example is shown in FIG.

  FIG. 6 is a diagram showing a configuration of a method using an LED light-emitting element called a side emitter type in which a light-emitting element itself is provided with a box-like reflecting member. FIG. 6A shows a main part centering on a light source part. FIG. 6B is a partial cross-sectional view showing the light source unit observed from the light guide plate. In FIG. 6B, the transparent sealing resin portion is omitted.

  The LED chip 221 is bonded on the element substrate 222, the reflection member 223 is provided around the LED chip 221 and sealed with a transparent sealing resin 224, and the side emitter type LED element 220 configured by providing the connection electrode 225 is formed on the substrate 270. Are arranged and connected to form a light source unit.

  The light source is fixed on the frame 260 so that the openings of the plurality of side-emitter LED elements 220 face each other in close proximity to the incident surface 211 of the light guide plate 210.

  With this configuration, the emitted light can be guided to the light guide plate while the light source unit is stably held at a predetermined position facing the light guide plate.

  In FIG. 6, 240 is a reflection sheet, and 250 is an optical film.

  As a method for obtaining planar light emission that can be used as a backlight from an LED that is a point light source, a method in which a large number of LEDs are arranged on an end surface of a light guide plate and light is directly input is generally used. Another example is shown in FIG.

  FIG. 7 is a diagram showing a configuration of a backlight in which a large number of high-power LED elements are arranged on the side surface of the light guide plate. FIG. 7A is a partial cross-sectional view showing the main part centering on the light source part. ) Is a top view of the light source section observed from the light guide plate.

  The LED element 520 includes an element substrate 522, an LED chip 521, and a condenser lens 524. A large number of LED elements 520 are linearly arranged on the wiring board 570. The reflecting member 523 has a U-shaped cross section, and the number of holes for allowing the condenser lens to be inserted is the same as the number of LED elements. An incident surface 511 of the light guide plate 510 is disposed so as to face a large number of LED elements 520 arranged in a straight line.

  In FIG. 7, reference numeral 540 denotes a reflection sheet, and 550 denotes an optical film. Patent Document 1 discloses a structure that efficiently and uniformly guides light from an LED, which is a point light source, to an incident end surface of a short-shaped light guide plate having a large aspect ratio.

By comprising in this way, the light from an LED element can be guide | induced to a light-guide plate.
JP 2004-235139 A

  A polarizing plate is disposed on the incident side of the liquid crystal panel, and only light having a specific polarization direction is used. About half of the light of the random polarization component from the cold cathode ray tube or the LED element is absorbed by the polarizing plate without being used.

  The author has found that the use of a laser with a uniform polarization direction and an illumination optical system can maintain the polarization direction, improve the light efficiency, and provide a bright liquid crystal display element.

  In view of the above problems, an object of the present invention is to provide a liquid crystal display device using a bright laser as a light source by improving light uniformity when a laser is used as a surface light source.

  In order to solve the above-described problems, it has been found that an illumination optical system including at least one laser, a light guide plate, and at least two lenses may be disposed.

  The surface light source of the present invention is characterized in that the light beam emitted from the laser is expanded to the shape of the incident end face of the light guide plate.

  The polarization direction of the light beam emitted from the laser is made to coincide with the polarization direction at the incident end face of the light guide plate.

  In this way, a surface light source with good light efficiency can be obtained when the polarization directions coincide with each other and the surface light source of the liquid crystal panel is used.

  The incident angle of the light beam incident on the light guide plate at the incident end surface of the light guide plate is made constant regardless of the position of the incident end surface of the light guide plate when viewed from the normal direction of the exit surface of the light guide plate.

  By doing in this way, the light ray inject | emitted from a light-guide plate becomes uniform within an emission surface, and the surface light source without a brightness nonuniformity is obtained.

  The illumination optical system is a telecentric optical system on the light guide plate side.

  By doing in this way, the light ray inject | emitted from a light-guide plate becomes uniform within an emission surface, and the surface light source without a brightness nonuniformity is obtained.

  The lens of the illumination optical system is constituted by a cylindrical lens.

  With this configuration, a minute circular light beam from the laser can be efficiently guided to the elongated and short incident end face.

  The illumination optical system is composed of an extender, and the magnification of the extender is set so as to be a ratio between the diameter of the light beam emitted by the laser and the length of the incident end face of the light guide plate.

  With this configuration, the laser light beam can be made into a parallel light beam having a large cross-sectional area, and the entire incident end face of the light guide plate can be illuminated, so that a surface light source having no brightness unevenness can be obtained.

  The illumination optical system is composed of a rod lens and a relay optical system. The relay optical system has a substantially conjugate relationship between the exit end face of the rod lens and the entrance end face of the light guide plate, and the lens constituting the relay optical system is composed of a cylindrical lens.

  By configuring in this way, the light amount unevenness possessed by the laser can be made uniform by the rod lens, and a surface light source free from brightness unevenness can be obtained.

  Light beams from a plurality of lasers are configured to enter the rod lens incident end face.

  By comprising in this way, the light of a some laser can be mixed uniformly, and a bright surface light source is made. Also, the laser can use different wavelengths of RGB, and the surface light source can be colored.

  An illumination optical system is composed of a plurality of lasers, two multi-lens arrays constituting the integrator, and a field lens.

  By comprising in this way, the light of a some laser can be mixed uniformly, and a bright surface light source is made. Also, the laser can use different wavelengths of RGB, and the surface light source can be colored.

  It has a fine adjustment mechanism that rotates the laser with respect to the optical axis of the illumination optical system.

  By doing so, the polarization direction of the laser can be adjusted to the polarization direction set by the liquid crystal panel, and a bright surface light source can be realized.

  In the surface light source of the present invention, an illumination optical system including at least one laser, a light guide plate, and at least two lenses is disposed, so that the polarization of the laser is maintained and light is effectively used in the liquid crystal panel. And a bright surface light source can be realized.

  Light beams from a plurality of lasers are configured to enter the rod lens incident end face.

  With this configuration, a plurality of lasers can be used, and the brightness can be improved. Moreover, a surface light source can be made into a color by making a several laser into the laser of another wavelength of RGB.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(Embodiment 1)
The configuration of the surface light source according to the first embodiment of the present invention is shown in FIG.

  FIG. 1 is a block diagram showing the configuration of the surface light source according to Embodiment 1 of the present invention. The light beam from the laser 101 is expanded by the extender, converted into a large light beam, and incident on the light guide plate. The extender includes an illumination optical system lens 201 and an illumination optical system lens 202. The ratio of the focal lengths of the illumination optical system lens 201 and the illumination optical system lens 202 is the enlargement ratio. This enlargement ratio is a ratio necessary for expanding the diameter of the light beam emitted from the laser 101 to the length of the incident end face 502 of the light guide plate 501.

  Since the light beam of the laser 101 is substantially circular and the incident end face 502 of the light guide plate 501 is short, the illumination optical system lens 201 and the illumination optical system lens 202 are cylindrical lenses in order to convert the circular shape into a short shape. Desirably configured.

  Parallel light beams are emitted from the laser 101 and collected by the illumination optical system lens 201. The focused position is away from the illumination optical system lens 201 by the focal length of the illumination optical system lens 201. The illumination optical system lens 202 is disposed at a position separated from the focal position of the illumination optical system lens 201 by the focal length of the illumination optical system lens 202. By arranging in this way, parallel light rays from the laser are expanded and incident on the incident end face 502 of the light guide plate 501. The incident angle is constant, that is, parallel regardless of the position of the incident end face 502. Light rays that have entered the incident end surface 502 of the light guide plate 501 are emitted from the emission surface 503.

  In this way, since parallel light beams emitted from a small area of the laser are converted into a large area and are incident on the incident end face 502 of the light guide plate 501, a uniform surface light source without illumination unevenness can be formed. In addition, since the illumination optical system does not disturb polarization, a surface light source with high light efficiency can be realized.

(Embodiment 2)
FIG. 2 is a configuration diagram showing the configuration of the surface light source according to Embodiment 2 of the present invention. The parallel rays emitted from the laser 101 are collected by the condenser lens 106. The condensing position is near the incident side end face of the rod lens 301. The shape of the end surface of the rod lens 301 is a rectangle. Multiple reflections are repeated inside the rod lens 301 and emitted from the exit end face of the rod lens 301. The exit end face of the rod lens 301 emits light having a uniform shape and a rectangular shape that is the same as the exit end face shape.

  It is the relay lens that guides the light beam on the exit end face of the rod lens 301 to the light guide plate 501. The relay lens includes illumination optical system lenses 203, 204, and 205. The relay lens is disposed so that the exit end face of the rod lens 301 and the entrance end face 502 of the light guide plate 501 are conjugated. By doing so, light can be efficiently guided.

  The illumination optical system lenses 203, 204, and 205 are cylindrical lenses configured to be telecentric on both sides, and light from the exit end face of the rod lens 301 is guided to the entrance end face 502 of the light guide plate 501.

  In this way, parallel light beams emitted from a minute area of the laser are mixed while being multiple-reflected by the rod lens 301, converted into a larger area and incident on the light guide plate 501, so that a uniform surface light source without illumination unevenness is obtained. it can.

(Embodiment 3)
FIG. 3 is a configuration diagram showing the configuration of the surface light source according to Embodiment 3 of the present invention. The parallel rays emitted from the laser 101 are collected by the condenser lens 106. The condensing position is near the incident side end face of the rod lens 302. The parallel light beams emitted from the laser 102 are collected by the condenser lens 106. The condensing position is near the incident side end face of the rod lens 302. The parallel light beams emitted from the laser 103 are collected by the condenser lens 106. The condensing position is near the incident side end face of the rod lens 302. The shape of the end surface of the rod lens 302 is a rectangle. Multiple reflections are repeated inside the rod lens 302 and emitted from the exit end face of the rod lens 302. The exit end face of the rod lens 302 emits light having a uniform shape and a rectangular shape that is the same as the exit end face shape. The illumination optical system lenses 203, 204, and 205 are configured to be telecentric on both sides, and light from the exit end face of the rod lens 302 is guided to the entrance end face 502 of the light guide plate 501.

  In this way, parallel light beams emitted from a small area of a plurality of lasers are mixed while being multiple-reflected by the rod lens 302, converted into a larger area and incident on the light guide plate, so that a uniform surface light source without uneven illumination is obtained. Can do. Since the output of a plurality of lasers can be mixed, the amount of light can be increased, and color display can be performed by using lasers having different RGB wavelengths.

(Embodiment 4)
FIG. 4 is a configuration diagram showing the configuration of the surface light source according to Embodiment 4 of the present invention. Two multi-lens arrays are arranged so as to constitute an integrator that reduces unevenness of light intensity of the light source. Parallel light beams emitted from the laser 101 are collected by the corresponding multi-lens array 401. The condensing position is near the multi-lens array 402. The direction of the light beam is changed by the multi-lens array 402, and the center of the light beam is directed to the center of the incident end face 502 of the light guide plate 501. The light emitted from the multi-lens array 402 diverges and illuminates the entire incident end face 502. By arranging in this way, an integrator is configured. The illumination optical system lens 206 collimates the divergent light emitted from the multi-lens array 402. This illumination optical system lens 206 has a role of a field lens. Similarly to the laser 101, the parallel light beams emitted from the lasers 102 to 105 illuminate the incident end face of the light guide plate.

  In this way, the parallel light beams emitted from the minute areas of the plurality of lasers are mixed by the multi-lens arrays 401 and 402, converted into a larger area and incident on the light guide plate 501, and therefore, a uniform surface light source without uneven illumination. Can do. Since the output of a plurality of lasers can be mixed, the amount of light can be increased, and color display can be performed by using lasers having different RGB wavelengths.

  In each of the above embodiments, a fine adjustment mechanism for rotating the laser with respect to the optical axis of the illumination optical system is provided, and fine adjustment is performed so that the polarization direction of the laser matches the polarization direction set by the liquid crystal panel. A brighter surface light source can be realized.

  The surface light source and the liquid crystal display device of the present invention have the effect of extracting light of uniform brightness with a uniform polarization direction from a laser, and are useful for liquid crystal monitors and particularly liquid crystal televisions that require color reproducibility. It is.

The block diagram which shows the structure of the surface light source in Embodiment 1 of this invention. The block diagram which shows the structure of the surface light source in Embodiment 2 of this invention. The block diagram which shows the structure of the surface light source in Embodiment 3 of this invention. The block diagram which shows the structure of the surface light source in Embodiment 4 of this invention. Top view and sectional view showing an edge input type backlight using a conventional cold cathode ray tube Cross-sectional view of a main part showing an edge input type backlight using a conventional side emitter LED light source element, and a top view of the light source part observed from the light guide plate side Cross-sectional view of the main part showing an edge-input type backlight using a conventional high-power LED light source element and a top view of the light source unit observed from the light guide plate side

Explanation of symbols

101-105 Laser 106, 524 Condenser lens 110, 210, 510 Light guide plate 111, 211, 511 Incident surface 112 Emission surface 113 Reflective surface 120 Cold cathode ray tube 130 Reflector 140, 540 Reflective sheet 150, 550 Optical film 201-206 Illumination Optical lens 220, 520 LED element 221, 521 LED chip 222, 522 Element substrate 223, 523 Reflective member 224 Sealing resin 225 Connection terminal 260 Frame 270, 570 Wiring substrate 301, 302 Rod lens 401, 402 Multi lens array 501 Optical plate 502 Entrance end face 503 Exit face

Claims (11)

At least one laser;
A light guide plate having an entrance end face and an exit face;
An illumination optical system composed of at least two lenses,
The surface light source characterized in that the illumination optical system has a function of expanding a light beam emitted from the laser into the shape of the incident end face and entering the incident end face. 2. The surface light source according to claim 1, wherein a polarization direction of a light beam emitted from the laser coincides with a polarization direction at the incident end face. 2. The surface light source according to claim 1, wherein an incident angle of a light beam incident on the incident end face is constant regardless of a position of the incident end face when viewed from a normal direction of the exit surface. 2. The surface light source according to claim 1, wherein the illumination optical system is telecentric on the light guide plate side. The surface light source according to claim 1, wherein the lens of the illumination optical system is constituted by a cylindrical lens. The said illumination optical system is comprised with the extender, The expansion ratio of the said extender is a ratio of the diameter of the light beam inject | emitted from the said laser, and the length of the incident end surface of the said light-guide plate, The said 1st aspect is characterized by the above-mentioned. Surface light source. The illumination optical system is composed of a rod lens and a relay optical system, and the relay optical system has a substantially conjugate relationship between the exit end face of the rod lens and the entrance end face of the light guide plate, and the lenses constituting the relay optical system are 2. The surface light source according to claim 1, wherein the surface light source is a cylindrical lens. The surface light source according to claim 7, wherein light beams from a plurality of lasers are incident on an incident end face of the rod lens. The laser is composed of a plurality of lasers,
The illumination optical system includes two multi-lens arrays constituting an integrator;
The surface light source according to claim 1, comprising a field lens. 10. The surface light source according to claim 8, further comprising a fine adjustment mechanism for rotating the laser with respect to the optical axis of the illumination optical system. A liquid crystal display device comprising the surface light source according to claim 1.

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