Patent Application
20070279934
The above and other aspects of the present invention will become more apparent by the following detailed description of exemplary embodiments thereof with reference to the attached drawings in which:
Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.
Referring to
The first layer 105 has an incident surface 105a, a surface 105b opposite the incident surface 105a, an upper surface 105c through which the light exits, and a lower surface 105d opposite the upper surface 105c.
In order to improve the efficiency of light exiting through the upper surface 105c and light polarization conversion, the light guide panel 140 includes a polarization converting plate 106 disposed on the lower part of the lower surface 105d, a lower reflective plate 107 disposed on the lower part of the polarization converting plate 106, and a side reflective plate 108 disposed on the surface 105b. In order to convert a polarization direction of incident light, a ¼-wavelength plate or other converting means can be used for the polarization converting plate 106 or the polarization converting plate 106 can be disposed on the side of the surface 105b.
The second layer 110 has a continuous and periodic array of exit units 115, each exit unit 115 including a first prism 112 and a second prism 114 that are adjacent to each other. Planar portions 111 are formed between the exit units 115.
The third layer 120 formed of anisotropic materials has different refractive characteristics according to a polarization direction of incident light. In other words, the third layer 120 has birefringence characteristics, i.e., first and second refractive indices with respect to light beams of first and second polarizations, respectively. Examples of the anisotropic materials may be PolyEthyleneTerephthalate (PET), PolyButylene-Terephthalate (PBT), and PolyEthyleneNaphthalate (PEN). The first and second layers 105 and 110 may be formed of an isotropic material having the same or almost the same refractive indices. For example, the first and second layers 105 and 110 may be formed of polymethyl methacrylate (PMMA) and resin having refractive indices of 1.49 and 1.5, respectively. In addition, the first and second layers 105 and 10 may be integrally formed of the same materials. The third layer 120 may have a first refractive index that is almost equal to those of the first and second layers 105 and 110 with respect to a light beam of P polarization and a second refractive index that is relatively larger than the refractive indices of the first and second layers 105 and 110 with respect to a light beam of S polarization. Therefore, there is no difference in the refractive indices at interfaces of each layer when a light beam of P polarization penetrates through the first through third layers 105, 110, and 120. The ideal case is when the first, second, and third layers 105, 110, and 120 have the same first refractive index and the second refractive index is relatively greater than the first refractive index. In this case, the light beam of P polarization travels through the first through third layers as if passing through a single layer of uniform material.
The exit unit 115 is formed of the first prism 112 and the second prism 114. The first and second prisms may each comprise at least two planar surfaces. In
In
The operation of the light guide panel 140 will now be described with reference to
Light emitted from the light source 100 is radiated in all directions. After light is incident on the first layer 105, the radiation range of the light is reduced according to the refractive index of the first layer 105. For example, when the refractive index of the first layer 105 is 1.49, light incident from air to the first layer 105 has a range of radiation angles of ±42 degree. Light transmitted downward from the first layer 105 is totally reflected at the lower part of the light guide panel 140 or is reflected at the lower reflective plate 107 to be transmitted upward. Also, light transmitted upward of the first layer 105 is refracted through the second layer 110. Light incident on the second layer 110 passes through the planar portion 111 and the first through fourth surfaces 112a, 112b, 114a, and 114b and is incident on the third layer 120. The first and second layers 105 and 110 are formed of isotropic materials and thus, are not affected by the polarization direction of incident light, while light incident on the third layer 120 has different refractive characteristics according to its polarization direction and thus, is transmitted along different paths according to its polarization direction. When a first refractive index ‘no’ of the third layer 120 with respect to light Ip of first polarization is substantially the same with the refractive index of the second layer 110 and a second refractive index ‘ne’ of the third layer 120 with respect to light Is of second polarization is greater than the refractive index of the second layer 110, the light Ip of the first polarization and the light Is of the second polarization are separated at the interface between the second layer and the third layer 120. The light Ip of the first polarization is incident on the third layer 120 at an angle greater than the critical angle and then is reflected from the top surface of the third layer 120, while the light Is of the second polarization is incident on the third layer 120 at an angle less than a critical angle and then is transmitted through a top surface of the third layer 120. That is, most of the incident light Is of the second polarization is transmitted at an angle that is almost perpendicular to the upper surface of the third layer 120.
In more detail, the operation of the light guide panel 140 with respect to light transmission of the second polarization, according to the position of the incident light at the interfaces of the second and third layers 110 and 120 is as follows. The light Ip of the first polarization passes through the first through the third layers without a change of the refractive index and thus, the light Ip is reflected from the upper surface of the third layer back toward the first layer. Hereinafter, light of the second polarization is described only.
Referring to
Third light L3, which is among the light traveling downward after being reflected from the upper surface of the third layer, is reflected from the planar portion 111 and then, is reflected again from the first planar surface 112a of the first prism 112 to exit through the top of the light guide panel. Fourth light L4, which is incident on the second planar surface 112b of the first prism 112, and is among the light reaching the first layer 105, is reflected from the second planar surface 112b and then, is totally reflected from the third planar surface 114a of the second prism 114 to exit through the top of the light guide panel.
When a portion of the light reaching the first layer 105 passes through the fourth planar surface 114b of the second prism 114, that light is totally reflected from the upper surface of the third layer 120 and exits through the top of the light guide panel along the same path as the third light L3.
As described above, since most light penetrating the planar portion 111 and the second planar surface 112b exits perpendicularly through the top of the light guide panel, both the amount of light exiting upwardly and the amount of light exiting perpendicularly are increased. The first prism 112 totally reflects the light incident on the first planar surface 112a of the first prism 112 with respect to the second prism 114, when the light does not satisfy the condition of total reflection.
Referring to
The first layer 205 has a first incident surface 205a on which light is incident from the first light source 200 and a second incident surface 205b opposite the first incident surface 205a on which light is incident from the second light source 201. In addition, according to the present embodiment, a reflective plate may be disposed instead of the second light source 201.
As illustrated in
The second layer 210 has a continuous and periodic array of exit units 215, each exit unit 215 including a first prism 212, a second prism 214, and a third prism 216. Planar portions 211 are formed between the exit units 215.
The first through third prisms 212, 214, and 216 may have the same size. In addition, the first and third prisms 212 and 216 may be smaller than the second prism 214. In this case, the first and third prisms 212 and 216 may have the same size as each other. When the first through third prisms 212, 214, and 216 have the same prism angles, the process of manufacturing the prisms can be simplified. The first and third prisms 212 and 216 totally reflect light emitted from the first and second light source 200 and 201. The second prism 214 reflects the light upwardly and the light exits through top of the third layer 220, wherein the light incident on the second prism 214 through the first and third prisms 212 and 216.
The third layer 220 formed of the anisotropic materials has different refractive characteristics according to a polarization direction of incident light. In other words, the third layer 220 has birefringence characteristics, i.e., first and second refractive indices with respect to light beams Ip and Is of first and second polarizations, respectively. The first refractive index is almost equal to that of the first and second layers 205 and 210 and the second refractive index is larger than that of the first and second layers 205 and 210. The light path of light emitted from the first light source 200 is separated at the interface between the second and third layers 210 and 220 according to light polarization.
Light emitted from the first light source 200 passes through the first and second layers 205 and 210 and the light path of light of the first and second polarization Ip and Is is changed at the first and second prisms 212 and 214 to be transmitted through the third layer 220. In addition, the light of the first polarization Ip is reflected from the upper surface of the third layer 220 toward the first layer 205 and the light of the second polarization Is exits through the upper surface of the third layer 220. On the other hand, light emitted from the second light source 201 passes through the first and second layers 205 and 210 and the light path of light of the first and second polarization Ip and Is is changed at the second and third prisms 214 and 216 to be transmitted through the third layer 220. In addition, the light of the first polarization Ip is reflected from the upper surface of the third layer 220 toward the first layer 205 and light of the second polarization Is exits through the upper surface of the third layer 220. Since the first and second prisms 212 and 214, with respect to the light emitted from the first light source 200, and the second and third prisms 214 and 216, with respect to the light emitted from the second light source 201, are the same with those described with respect to
The first prism 212 and the third prism 216 can be symmetrical with respect to the second prism 214 and operate in the same manner for light emitted from first and second light sources 200 and 201. A polarization converting plate and a reflective plate (not illustrated) may be further disposed on the lower surface of the first layer 105.
Referring to
The backlight unit 150 further includes a diffusion plate 153 which diffuses light, a first prism sheet 155 which corrects the transmitting path of light, and a second prism sheet 157 disposed between the light guide panel 140 and the display panel 170. The first and second prism sheets 155 and 157 are arranged perpendicular to each other and thus, refract and focus light output from the diffusion plate 153 in order to improve the directionality of the light, thereby increasing the light brightness and reducing the incident angle of light. Optical sheets and components disposed between the light guide panel 140 and the display panel 170 can exhibit better performances when they can conserve polarization direction. According to the characteristics of light exiting from the display panel, the display panel can be assembled without using the first and second prism sheets 155 and 157 and the diffusion plate 153.
The display panel 170 may be an LCD panel. The LCD panel uses only light of a specific polarization as effective light. In the present invention, the light is separated at the third layer 120 included in the light guide panel which is formed of anisotropic materials and thus, only a light beam having specific polarization exits upwardly from the third layer 120. Therefore, a separate polarizing film for separating polarizations is not required. In addition, a polarization converting plate 106 and a reflective plate 107 may be further included on the lower surface of the first layer 105 to improve light efficiency.
As described above, the light guide panel according to exemplary embodiments of the present invention includes a plurality of exit units including a plurality of prisms and planar portions between the exit units to increase the amount of light exiting both upwardly and perpendicularly, thereby achieving high output power.
A backlight unit employing the light guide panel according to exemplary embodiments of the present invention provides images of high brightness with high output power. The backlight unit includes a layer formed of an anisotropic material on the upper surface of the light guide panel to separate light of different polarizations at the light guide panel and thus, only a light beam of one polarization is allowed to exit upwardly. Therefore, the backlight unit has a simple structure since a separate polarizing film for separating lights of different polarizations is not required.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0049994 | Jun 2006 | KR | national |
