Optical waveguides – Planar optical waveguide
Patent
1998-06-25
2000-12-26
Ullah, Akm E.
Optical waveguides
Planar optical waveguide
G02B 610
Patent
active
061671827
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a surface light source device used for a liquid crystal display device, a lighting device or the like, and a liquid crystal display device, a portable telephone and an information terminal using the surface light source device.
BACKGROUND ART
A conventional surface light source device is illustrated in FIGS. 1 and 2. FIG. 1 is an exploded perspective view, and FIG. 2 is a cross-sectional view. A surface light source device 1 comprises an optical (wave)guide plate 2 for confining and propagating light, a light emitting device 3, and a reflecting plate 4. The optical guide plate 2 is formed of resin which is transparent and has a high index of refraction, for example, polycarbonate resin or methacrylic resin, and a diffuse pattern 5 is formed by irregular processing, dot printing of diffuse reflective ink or the like on the lower surface of the optical guide plate 2. The light emitting device 3 is one having a plurality of so-called point light sources 7, for example, light emitting diodes (LED) mounted on a circuit board 6, and is opposite to an end surface (a light incidence surface 8) of the optical guide plate 2. The reflecting plate 4 is formed of a white resin sheet, for example, which has a high index of reflection, and is affixed to the lower surface of the optical guide plate 2 on both its sides by double-sided tapes 9.
Light emitted from the light emitting device 3 and introduced into the optical guide plate 2 from the light incidence surface 8 is confined in the optical guide plate 2 and travels by being totally reflected from the inside of the optical guide plate 2. The light inside the optical guide plate 2 is diffuse reflected upon impinging on the diffuse pattern 5. A light beam f1, incident on a light output surface 10 at a smaller angle than the critical angle in the total reflection, of the reflected light beams is emitted outward from the light output surface 10. A light beam f2 passing through a portion, where the diffuse pattern 5 does not exist, on the lower surface of the optical guide plate 2 is returned to the optical guide plate 2 again upon being reflected from the reflecting plate 4, so that the loss of the quantity of light on the lower surface of the optical guide plate 2 is prevented from occurring.
In the conventional surface light source device 1, however, a light beam f3, entering a portion between the lower surface of the optical guide plate 2 and the reflecting plate 4, of the light beams emitted from the light emitting device 3 enters the optical guide plate 2 from the lower surface of the optical guide plate 2 upon being reflected from the reflecting plate 4, and is emitted from the light output surface 10 of the optical guide plate 2 without being totally reflected, as shown in FIG. 3. Therefore, the intensity of the output light is large in the vicinity of the light incidence surface 8, as shown in a graph of light output intensity characteristics on the light output surface 10 in FIG. 4. As a result, the luminance of the emitted light is high in the vicinity of the light incidence surface 8 (an area where the luminance is high is indicated by reference numeral 11), and the degree of non-uniformity of the luminance distribution on the light output surface 10 of the optical guide plate 2 is high.
In the surface light source device 1, a linear light source such as a cold-cathode ray tube or a hot-cathode ray tube is replaced with the point light sources 7 such as light emitting diodes in order to reduce the power consumption. The point light sources 7 such as light emitting diodes are disposed in line and brought into a pseudo linear light source. Used is the optical guide plate 2 which is fabricated in accordance with the same design philosophy as that in a case where the linear light source is used. Particularly, the diffuse pattern 5 on the optical guide plate 2 is the same as that in the case where the linear light source is used. That is, reflecting elements 5a constituting the diffuse pattern 5 are disposed in a
REFERENCES:
patent: 5481515 (1996-01-01), Kando et al.
patent: 5593913 (1997-01-01), Akio
patent: 5691548 (1997-11-01), Akio
Aoyama Shigeru
Shinohara Masayuki
Omron Corporation
Ullah Akm E.
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