CN100419530C - Surface light source device and liquid crystal display - Google Patents

Abstract

The invention relates to a surface light source device and a liquid crystal display. The surface light source device includes a light guide plate, at least one light source and a plurality of diffraction grating units. surface, the at least one light source is arranged adjacent to the light incident surface, and the plurality of diffraction grating units are arranged on the bottom surface of the light guide plate, which include two kinds of grating regions with different arrangement directions, and the diffraction grating units are adjacently arranged and cover the entire bottom surface of the light guide plate .

Description

Surface light source device and liquid crystal display

【Technical field】

The invention relates to a surface light source device and a liquid crystal display using the surface light source device, in particular to a surface light source device and a liquid crystal display with a grating structure on the bottom of a light guide plate.

【Background technique】

The surface light source device in the prior art liquid crystal display includes a light source and a light guide plate. The light source is arranged relative to the light incident surface of the light guide plate. . A plurality of dots are distributed on the bottom surface of the light guide plate to scatter the light beam transmitted inside the light guide plate, so as to improve the uniformity of the light beam emitted from the light guide plate. In order to improve the problem of poor light uniformity of dots, recently, diffraction grating technology is used in light guide plates to improve light uniformity of light guide plates.

For a surface light source device using diffraction grating technology, please refer to US Patent No. 5,703,667 published on December 30, 1997. Please refer to FIG. 1, the surface light source device 1 includes a light guide plate 2, a fluorescent lamp 4 arranged adjacent to the incident surface 2c of the light guide plate 2, a reflector 5 arranged adjacent to the bottom surface 2b of the light guide plate 2, and a reflector 5 arranged on the light guide plate 2. 2 The diffusion plate 6 and the prism plate 7 on the side of the light emitting surface 2a. The bottom surface 2b of the light guide plate 2 has a single arrangement of diffraction grating structures 3 parallel to the fluorescent lamps 4 . Because the light emitted from the fluorescent lamp 4 is white light, and due to the diffraction effect, the part of the diffracted light emitted from the light emitting surface 2a can be basically separated into RGB three-color light and emitted. The RGB three-color light diffuses through the diffusion plate 6 and remixes into white. Changing the ratio of the grating 3 to the non-grating area 3 ′ within a unit length along the direction away from the fluorescent lamp 4 can improve the light uniformity of the light guide plate 2 . However, there are deficiencies in this patented technology.

Firstly, the uniformity of light output from the light output surface 2 a of the light guide plate 2 is still insufficient. The reason is that the gratings of the grating structure 3 are in a single arrangement structure, and after the incident light is diffracted, the diffracted light will be perpendicular to the single grating arrangement and exit the light-emitting surface 2a. That is, the single grating arrangement makes the direction of the light emitted from the light emitting surface 2a mainly lie in the plane perpendicular to the grating arrangement, which limits the range of the light emitting direction of the light guide plate 2 and narrows the viewing angle range when it is applied to a liquid crystal display.

Secondly, the light diffraction efficiency of the bottom surface 2b of the light guide plate 2 is insufficient, that is, the non-grating region 3' of the bottom surface 2b of the light guide plate 2 will not diffract the incident light. In order to control the uniformity of light output, the bottom surface 2b of the light guide plate 2 is not completely covered by the grating structure 3, but there is a non-grating area 3'. However, the grating area 3' cannot allow light to exit from the light output surface 2a. Therefore, its corresponding light output The portion of the surface 2 a is darker than the portion of the light-emitting surface 2 a corresponding to the grating structure 3 .

【Content of invention】

In order to overcome the defect of non-uniform light output of the surface light source device in the prior art, the present invention provides a surface light source device with high uniformity of light output.

The present invention also provides a liquid crystal display with high optical performance using the surface light source device.

The technical solution adopted by the present invention to solve the technical problem is to provide a surface light source device, which includes a light guide plate, at least one light source and a plurality of diffraction grating units, the light guide plate includes a light exit surface, and a light exit surface opposite to the light exit surface. The bottom surface of the light guide plate and at least one light incident surface connected to the light exit surface and the bottom surface, the at least one light source is arranged adjacent to the light incident surface, and the plurality of diffraction grating units are arranged on the bottom surface of the light guide plate, which includes two A grating area, the diffraction grating unit is arranged adjacently and covers the entire bottom surface of the light guide plate.

The present invention also provides a liquid crystal display, which includes a liquid crystal panel and the above-mentioned surface light source device, and the liquid crystal panel is arranged on one side of the light-emitting surface of the light guide plate.

Compared with the prior art, the present invention has the following advantages: the plurality of diffraction grating units on the bottom surface of the light guide plate of the surface light source device of the present invention have two kinds of grating regions with different arrangement directions, and the two kinds of grating regions can make the incident light from different directions The light is diffracted, and the two kinds of diffracted light are located in different light-emitting planes, thereby improving the uniformity of light output of the light guide plate and the surface light source device using the light guide plate. Because the liquid crystal display of the present invention adopts the surface light source device, its viewing angle range is relatively large.

【Description of drawings】

Fig. 1 is a schematic diagram of a surface light source device in the prior art.

Fig. 2 is a schematic diagram of the surface light source device of the present invention.

3 is a cross-sectional view of a light guide plate and a schematic diagram of an optical path of the surface light source device of the present invention.

Fig. 4 is a schematic diagram of light output of the surface light source device of the present invention.

【Detailed ways】

Referring to FIG. 2 and FIG. 3 , the surface light source device 30 of the present invention includes a light guide plate 31 and a light source 32 . The light guide plate 31 includes a light emitting surface 313 , a bottom surface 312 opposite to the light emitting surface 313 , a light incident surface 311 connected to the light emitting surface 313 and the bottom surface 312 , and a plurality of side surfaces 314 . The light source 32 is a line light source such as CCFL (Cold Cathode Fluorescent Lamp, Cold Cathode Fluorescent Lamp), of course, it can also be a point light source such as LED (Light Emitting Diode, Light Emitting Diode), which is arranged adjacent to the light incident surface 311 of the light guide plate 31. In addition, the surface light source device 30 further includes a reflective plate (not shown) disposed adjacent to the bottom surface 312 of the light guide plate 31 .

The light incident surface 311 receives the light from the light source 32 and guides it into the light guide plate 31 . The light emitting surface 313 guides the light out of the light guide plate 31 . The side surface 314 is a reflective surface, which reflects the incident light back to the light guide plate 31 and exits through the light emitting surface 313 .

The bottom surface 312 of the light guide plate 31 is provided with a plurality of diffraction grating units 33 integrally formed with the light guide plate 31 , which are arranged adjacent to each other and cover the entire bottom surface 312 of the light guide plate 31 . Each diffraction grating unit 33 includes two kinds of grating regions A and B with different grating arrangement directions. The grating section of the diffraction grating unit 33 is rectangular, and its grating constant P is 2-10 μm, preferably 3 μm; the corresponding rectangular width W It is 1 to 5 μm, preferably 1.5 μm.

Please refer to the area enlarged diagrams I and II in Figure 2, the gratings of the juxtaposed A and B grating areas are arranged perpendicular to each other, the grating arrangement of the A grating area is parallel to the light incident surface of the light guide plate, and the A grating area occupies the entire diffraction grating unit The ratio of the area of 33 increases the farther away from the light source 32 . The function of the diffraction grating unit 33 is to diffract the light L to make the light emitting surface 313 of the light guide plate 31 emit light evenly.

The light guide plate 31 is made of transparent material, such as acrylic resin, polycarbonate, polyethylene resin or glass, and its refractive index is greater than 1, such as 1.54. Since the refractive index of the light guide plate 31 is greater than 1, after the light L perpendicular to the light incident surface 311 enters the light guide plate 31, when the incident angle of the light incident on the diffraction grating unit 33 is greater than the total reflection angle, due to the B grating area of the diffraction grating unit 33 Parallel to the light L, so the light L incident on the B grating area is totally reflected by the bottom surface 312, and then totally reflected on the light exit surface 313, so that it will not exit from the light exit surface 313 of the light guide plate 31; and the light L is vertically incident on the A grating In the A grating area, since the grating arrangement in the A grating area is perpendicular to the incident light L, light L is diffracted on a plane (the first plane) perpendicular to the grating arrangement direction in the A grating area. The incident angle θ of light L ₁ with a lower diffraction order to the light exit surface 313 is smaller than the total reflection angle, so it exits from the light exit surface 313, while the light rays L ₂ and L ₃ with higher diffraction orders are incident to the light exit surface 313. The incident angle of the surface 313 is larger than the total reflection angle, so it is totally reflected by the light-emitting surface 313 and continues to propagate in the light guide plate 31 until the next diffraction occurs and emerges from the light-emitting surface 313 .

Light _L1 with a lower diffraction order accounts for most of the energy of light L, and the light emitted from the light-emitting surface 313 of the light guide plate 31 has a certain directionality, and the grating parameters in the B grating area, such as the grating constant P, can control the light Diffraction efficiency of L. Therefore, the diffraction grating unit 33 has better light utilization rate and light emission direction than the dot structure of the prior art, and the resolution of the diffraction grating unit 33 is higher, and the light guide plate 31 adopting this technology has a higher light emission uniformity.

Similarly, the B grating area also diffracts the incident light perpendicular to the arrangement direction of the B grating area on the plane (second plane) perpendicular to the grating arrangement direction of the B grating area, and a part of the diffracted light can exit from the light exit surface 313 . Please refer to FIG. 4, the diffracted light rays generated by the A and B grating regions are located in different light-emitting planes (the first and second planes, that is, the plane defined by the X-axis and the Z-axis and the plane defined by the Y-axis and the Z-axis respectively), so The intensity of light emitted from each direction of the light-emitting surface 313 of the light guide plate 31 is relatively balanced, that is, the uniformity of the light emitted by the light guide plate 31 is relatively high, and the bottom surface 312 of the light guide plate 31 is covered by the continuous diffraction grating unit 33, so the utilization rate of light is improved. In addition, in order to cope with the situation that the bottom surface 312 receives uneven light due to the different distances between each part of the light guide plate 31 and the light source 32, or the limited light emitting angle of the light source 32, the ratio of the A grating area to the entire area of the diffraction grating unit 33 is further away from the light source 32. The larger, or the area ratio of the bottom surface 312 of the light guide plate 31 corresponding to the two ends of the light source 32 is larger, so that the light output capability of the light output surface 313 corresponding to the A grating area is inversely proportional to the light intensity incident to the A grating area, further improving the light guide plate 31. Light uniformity. Therefore, the surface light source device 30 of the present invention has better light uniformity and light utilization rate than the prior art.

In addition, the grating constant P of each diffraction grating unit 33 can also be changed, thereby changing the diffraction efficiency of each diffraction grating unit 33 to achieve the purpose of uniform light output, such as changing the grating constant so that it becomes smaller as it is farther away from the light source 32 .

According to the present invention, the diffraction grating unit 33 can also be shown in the enlarged area III and IV of FIG. 2 , the grating is inclined to the light incident surface 311 of the light guide plate 31 , and the A and B grating areas are nested. For the situation that the grating is inclined to the light incident surface 311 of the light guide plate 31, the grating inclination angle of the A and B grating regions can be adjusted, the gratings of the A and B grating regions are arranged to be non-perpendicular, and the area ratio of the A and B grating regions is designed to make the diffraction The ratio of the area of the grating unit 33 perpendicular to the incident light L to the other portion is inversely proportional to the intensity of the incident light L. According to the present invention, the plurality of diffraction grating units 33 can also be separated so that they are distributed on the bottom surface 312 of the light guide plate 31 according to a certain rule; the grating section of the diffraction grating unit 33 can also be arc-shaped or V-shaped, and the grating constant is 2-10 μm; the light guide plate 31 can have multiple light incident surfaces 311 , that is, the side surfaces 314 can also be light incident surfaces 311 , and multiple light sources 32 are provided corresponding to the multiple light incident surfaces 311 .

The plurality of diffraction grating units 33 are formed integrally with the light guide plate 31 by molding technology, and the pattern on the surface of the mold core corresponding to the diffraction grating units 33 is made by electron beam exposure technology or nano-process. The diffraction grating unit 33 can be printed on the bottom surface 312 of the light guide plate 31 by printing method, or can be attached to the light guide plate by using an optical film with multiple diffraction grating units 33 structures. 31 bottom surface 312 .

The present invention also provides a liquid crystal display (not shown), which includes a liquid crystal panel and the aforementioned surface light source device 30 , and the liquid crystal panel is disposed on the side of the light-emitting surface 313 of the light guide plate 31 .

Claims (12)

1. planar light source device, it comprises a light guide plate, at least one light source and a plurality of diffraction grating unit, this light guide plate comprises an exiting surface, one and the incidence surface that joins with this exiting surface and this bottom surface of the bottom surface that is oppositely arranged of this exiting surface and, contiguous this incidence surface of this at least one light source is provided with, this a plurality of diffraction grating unit is arranged at this bottom surface of light guide plate, it is characterized in that: this diffraction grating unit comprises two kinds of grating regions that orientation is different, this adjacent setting in diffraction grating unit and cover whole bottom surface of light guide plate.

2. planar light source device as claimed in claim 1 is characterized in that: the mutual homeotropic alignment of the grating of these two kinds of grating regions.

3. planar light source device as claimed in claim 2 is characterized in that: its grating of the grating region in these two kinds of grating regions is arranged and is parallel to the light guide plate incidence surface.

4. planar light source device as claimed in claim 3 is characterized in that: this area of grating region that is parallel to the light guide plate incidence surface is big more away from light source more.

5. planar light source device as claimed in claim 3 is characterized in that: this grating constant of grating region that is parallel to the light guide plate incidence surface is more little away from light source more.

6. planar light source device as claimed in claim 2 is characterized in that: the grating in these two kinds of grating regions is arranged and is favoured the light guide plate incidence surface.

7. planar light source device as claimed in claim 1 is characterized in that: these two kinds of grating regions are inversely proportional to perpendicular to the part of light incident area ratio and the intensity of incident light with other parts.

8. planar light source device as claimed in claim 1 is characterized in that: this a plurality of diffraction grating unit is one-body molded or adopt printing process to be printed in this bottom surface of light guide plate or be that an optical thin film is attached at this bottom surface of light guide plate with this light guide plate.

9. planar light source device as claimed in claim 1 is characterized in that: two kinds of grating regions in this diffraction grating unit are for being set up in parallel or nested setting.

10. planar light source device as claimed in claim 1 is characterized in that: the grating section of this diffraction grating unit is rectangle or arc, and its grating constant is 2～10 μ m, and section is that the rectangle width of the grating of rectangle is 1～5 μ m.

11. planar light source device as claimed in claim 1 is characterized in that: the grating section of this diffraction grating unit is rectangle or arc, and its grating constant is 3 μ m, and section is that the rectangle width of the grating of rectangle is 1.5 μ m.

12. a LCD, it comprises a liquid crystal panel, it is characterized in that: this LCD at least also comprises one as each described planar light source device in the claim 1 to 8, and this liquid crystal panel is arranged at this light guide plate exiting surface one side.

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