Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
1999-09-10
2002-01-22
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S061000, C349S117000, C349S137000
Reexamination Certificate
active
06340999
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflective type liquid crystal display apparatus used in information display systems, office automation equipment, or the like, and to a front light for illuminating the same without deteriorating the display quality thereof.
2. Description of the Related Art
Typically, a reflective type liquid crystal display apparatus includes a reflective type liquid crystal display device (a liquid crystal panel) having a pair of glass substrates and a liquid crystal layer interposed therebetween. One of the glass substrates on the rear side of the reflective type liquid crystal display device is provided with a reflector. The other substrate on the light introduction side of the reflective type liquid crystal display device is provided with a polarization selecting section including a polarization plate, a quarter-wave plate, etc. While incident light transmitted through the polarization selecting section is reflected by the reflector, the polarization of the incident light is modulated by the liquid crystal layer. Thus, the amount of light which is output from the reflective type liquid crystal display device through the polarization selecting section is controlled, thereby displaying images.
Hereinafter, typical transitions of the polarization of light passing through this reflective type liquid crystal display apparatus will be described with reference to FIG.
14
.
The reflective type liquid crystal display apparatus has a reflective type liquid crystal display device
65
, in which a liquid crystal layer
66
is interposed between a pair of glass substrates
65
a
and
65
b,
and a reflector
67
is provided between the rear-side glass substrate
65
b
and the liquid crystal layer
66
. On the front side of the reflective type liquid crystal display device
65
, a polarizing plate
64
a
and a quarter-wave plate
64
b
are provided such that a transmission axis (or an absorption axis) of the polarizing plate
64
a
makes an angle of about 45° with a slow axis (or a fast axis) of the quarter-wave plate
64
b.
A portion of incident light (linearly polarized light) transmitted through the polarizing plate
64
a
is converted to circularly polarized light by the quarter-wave plate
64
b
and incident upon the reflective type liquid crystal display device
65
. When the liquid crystal layer
66
of the reflective type liquid crystal display device
65
does not modulate the incident circularly polarized light, the rotary direction of the circularly polarized light is inverted as the light is reflected by the reflector
67
. Then, the light is again transmitted through the quarter-wave plate
64
b
(upwardly in
FIG. 14
) and is converted to linearly polarized light having a polarization direction A at about 90° with the transmission axis of the polarizing plate
64
a.
Thus, the light is absorbed by the polarizing plate
64
a,
resulting in a black display.
On the other hand, when the liquid crystal layer
66
modulates the incident circularly polarized light, the light may be reflected by the reflector
67
and exit the reflective type liquid crystal display device
65
with the original circular polarization. Then, the light, after passing through the quarter-wave plate
64
b
again, becomes linearly polarized light whose direction of polarization B is identical with the direction of the transmission axis of the polarizing plate
64
a
so as to be transmitted through the polarizing plate
64
a,
resulting in a white display.
The directions of the transmission axis of the polarizing plate
64
a
and the slow axis of the quarter-wave plate
64
b
are determined in view of the liquid crystal material, the orientation of the liquid crystal material, the viewing angle characteristic, etc. Furthermore, in order to compensate for the tolerance of the phase delay with respect to the wavelength of the light output from the quarter-wave plate
64
b,
a half-wave plate may be provided between the polarizing plate
64
a,
and the quarter-wave plate
64
b.
The polarizing plate, the half-wave plate, and the quarter-wave plate are usually integrated together via adhesive layers, and further attached to the reflective type liquid crystal display device via another adhesive layer.
Furthermore, when images are displayed in colors by this reflective type liquid crystal display apparatus, light is transmitted through a color filter layer including color filter portions of three primary colors, i.e., red, green, and blue, which are provided in each pixel, whereby colored light can be obtained. Among various RGB arrangements, a delta arrangement as shown in
FIG. 15A and a
stripe arrangement as shown in
FIG. 15B
are commonly used. In these color filter arrangements, a unit pattern (corresponding to one pixel) comprising the three primary color portions is repeated in the vertical and horizontal direction.
Also, the number of pixels provided and the size of each pixel vary for different specifications. For example, for a 2.0″ reflective type liquid crystal display apparatus employing a delta arrangement, the number of pixels is 280×220 (horizontal×vertical), the pixel size is 145.5 &mgr;m in the horizontal direction and 138.5 &mgr;m in the vertical direction. For a 2.5″ display, the number of pixels is 280×220 (horizontal×vertical), and the pixel size is 179.5 &mgr;m in the horizontal direction and 168.5 &mgr;m in the vertical direction. For a 3.8″ QVGA reflective type liquid crystal display apparatus, pixels are patterned in a stripe arrangement, the number of pixels is 960×240 (horizontal pixels×vertical pixels), and the pixel size is 81 &mgr;m in the horizontal direction and 234.5 &mgr;m in the vertical direction.
A reflective type liquid crystal display apparatus can display images using ambient light. However, since the brightness of the display is significantly dependent on the environment in which the apparatus is used, the displayed images may not be perceived at all, especially in the dark, e.g., at night.
Thus, for cases where sufficient ambient light cannot be obtained, a type of illuminator, called a “front light”, for illuminating a reflective type liquid crystal display device from the front side thereof, has been proposed in the art.
For example, in SID '95 DIGEST, p.375, a front light as shown at reference numeral
81
in
FIG. 16
is disclosed.
The front light
81
includes a light guide
83
and a light source
82
placed on an end surface of the light guide
83
. An upper surface
83
c
opposite to a lower surface
83
b
of the light guide
83
includes periodic concave and convex portions. Light is output from the light source
82
and propagates through the light guide
83
. The light may be reflected by the upper surface
83
a
one time so as to exit the light guide
83
or may be totally reflected by the lower surface
83
b
and/or the upper surface
83
c
several times while propagating through the light guide
83
, so as to be reflected by the periodic concave-convex portions light guide
83
thereby exiting the lower surface
83
b.
Thereafter, the light output from the lower surface
83
b
is incident on a reflective type liquid crystal display device
85
, to which the polarization selecting section
84
including a polarizing plate and a quarter-wave plate is attached via an adhesive layer
90
.
However, when the above-described front light
81
is ON, some of the output light leaks through the upper surface
83
c
of the light guide
83
to directly reach the viewer's eye, whereby the black display is degraded because of the light leakage. This significantly deteriorates the contrast of the display. Furthermore, the light leaking through the upper surface
83
c
may be incident on a foreign material such as dust in the vicinity of the upper surface
83
c
or a flaw on the surface of the light guide
83
, which is then observed as a bright spot. In addition, the leak light may also be incident on a foreign material present b
Ebi Tsuyoshi
Masuda Takeshi
Sumida Yukihiro
Ngo Julie
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Sikes William L.
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