Illumination – Revolving
Reexamination Certificate
1999-06-15
2001-05-22
Tso, Laura K. (Department: 2875)
Illumination
Revolving
Reexamination Certificate
active
06234639
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polarization converter which produces polarized light having an identical polarization direction, and to a lighting device for an LCD panel using the polarization converter.
2. Description of the Related Art
In a liquid crystal display in which a liquid crystal display element (LCD panel) must be illuminated with polarized light having an identical polarization direction (linearly polarized light), various kinds of polarization converters are used. In particular, an LCD panel for a notebook personal computer, a digital camera or a video camera is illuminated using a thin lighting device (backlight). In general, in a known backlight in which unpolarized light from a light source is transmitted through a wedge-shaped light guide element and is emitted outside from one surface thereof, a polarization converter is provided between the emission surface of the light guide element and the LCD panel. The polarization converter absorbs 100% of light of a specific polarization direction (oscillation direction) from unpolarized light, the oscillation direction thereof being random, and permits a polarized light component whose polarization direction is perpendicular to the specific polarization direction to pass therethrough. Therefore, there is an inevitable light energy loss of at least 50%.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a polarization converter in which the utilization efficiency of light energy can be enhanced, i.e., more than 50% of light energy being utilized; and also to provide a lighting device for an LCD panel using the polarization converter.
Another object of the present invention is to provide a polarization converter in which the light-quantity distribution can be made as uniform as possible, and to provide a lighting device for an LCD panel using the polarization converter.
According to an aspect of the present invention, there is provided a polarization converter having a planar light guide element, in which at least one of front and rear surfaces thereof defines a light emission surface and one end surface defines an initial edge surface for an unpolarized light source, the light from the unpolarized light source propagating in a principal guided-light direction within the planar light guide element so that light incident upon the initial edge surface can be emitted from the light emission surface; wherein at least one corrugated (wave-shaped, zigzag) reflection surface is provided within the light guide element; the corrugated reflection surface defining a plurality of reflection surfaces arranged in the principal light guide direction; the corrugated reflection surface is formed by at least two adjacent optical media having different refractive indexes, and wherein the corrugated reflection surface is formed so that normal vectors of each of the plurality of reflection surfaces are within a normal plane.
Preferably, the refractive indexes n of the optical media are both greater than 1 (N>1).
Preferably, the respective refractive indexes n&agr;, n&bgr; of each optical media satisfy the following equation:
|n&agr;−n&bgr;|/(n&agr;+n&bgr;)<0.16.
Preferably, the reflection surfaces of the corrugated reflection surface includes externally-reflecting surfaces which reflect light therefrom, and emit the light from the light emission surface or emit the light from the rear surface; and internally-reflecting surfaces which reflect the light propagating through the light guide to thereby maintain the light reflected therefrom within the light guide element.
Preferably, the density of the externally-reflecting surfaces increases in a direction from the initial edge surface toward a final edge surface provided at the opposite end of the initial edge surface, and the density of the internally-reflecting surface decreases in a direction from the initial edge surface toward the final edge surface.
Preferably, the externally-reflecting surfaces of the corrugated reflection surface include first oblique portions which reflect the light toward the light emission surface, and second oblique portions which reflect the light toward a rear surface which is a surface provided opposite to the light emission surface.
Preferably, the light guide element includes a reflection surface provided opposite to the light emission surface, which reflects the light emitted from the rear surface back into the light guide element.
Preferably, at least one of the optical media which constitutes the corrugated reflection surface includes an adhesive.
Preferably, at least two optical media that constitute the corrugated reflection surface are made of a pair of glass or plastic members which form the light guide element, and wherein the adhesive adheres the glass or plastic members together.
Preferably, at least two optical media that constitute the corrugated reflection surface are made of at least one synthetic resin film and an adhesive, held between a pair of glass or plastic members which form the light guide.
Preferably, the period s of the corrugated reflection surface is considerably larger than the wavelength &lgr; of the unpolarized light introduced in the light guide element (s>&lgr;).
The light guide element can include a reflection surface provided opposite to the final edge surface, which reflects the light emitted from the final edge surface back into the light guide element.
A quarter-wave plate can be further provided between the final edge surface of the light guide element and the reflection surface.
Alternatively, the inclination of the normals of first oblique portions of the corrugated reflection surface with respect to the principal guided-light direction are gradually varied so that the incident angle of the light upon the oblique portion is small on the initial edge surface side and increases in a direction towards the final edge surface.
Alternatively, the light guide element can be in the form of a wedge whose thickness decreases in a direction away from the initial edge surface toward the final edge surface.
Alternatively, the refractive index of the adhesive can gradually increase in a direction away from the initial edge surface toward the final edge surface.
The positional density of the first oblique portions of the corrugated reflection surface can increase in a direction away from the initial edge surface to the final edge surface.
Alternatively, the light guide element can be made of a birefringent substance.
Alternatively, the light guide element can be made of an optically active substance.
The final edge surface can be a roof mirror group which is opposite to the initial edge surface, the roof mirror group having ridges inclined at 45° with respect to a direction normal to the light emission surface.
Alternatively, a roof mirror group having ridges parallel with the light guide direction of the light guide element can be provided between the light emission surface of the light guide element and the surface opposite the light emission surface.
Preferably, the apex angle of the roof mirror group is 90°.
Preferably, the light guide element is provided with a pair of light guide members having mutually engageable depressions and projections that determine the direction of the corrugated reflection surface, at least one corrugated reflection surface being defined by the pair of light guide members and an adhesive layer provided between the mutually engageable depressions and projections of the light guide members to thereby adhere the light guide members together.
Alternatively, the light guide element can be provided with a pair of light guide members having mutually engageable depressions and projections that determine the direction of the corrugated reflection surface, the at least one corrugated reflection surface being defined by a synthetic resin film and an adhesive layer, provided between the mutually engageable depressions and projections of the light guide elements.
Preferably, the synthetic resin fi
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Tso Laura K.
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