Illumination – With polarizer
Reexamination Certificate
2003-03-14
2004-12-21
Cariaso, Alan (Department: 2875)
Illumination
With polarizer
C362S035000, C362S330000, C362S561000
Reexamination Certificate
active
06832840
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device, and more particularly to a display device having a front light.
2. Description of the Background Art
In recent years, liquid crystal display devices, having desirable characteristics such as a small thickness and a small power consumption, have been widely used in various applications, including OA equipment such as word processors and personal computers, PDAs (personal digital assistance) such as electronic organizers, and camcorders with liquid crystal monitors.
Unlike a self-luminous display device such as a CRT (Cathode Ray Tube), a PDP (Plasma Display Panel) and an EL (Electro Luminescence) device, a non-luminous type display device such as a liquid crystal display device does not emit light by itself, and displays characters and images by controlling the amount of externally-provided light to be transmitted or reflected.
These liquid crystal display devices are generally classified into those of transmission type and those of reflection type.
A transmission type liquid crystal display device displays an image by modulating light from an illuminator (so-called “backlight”) arranged on the rear side of a liquid crystal display element through a liquid crystal layer of the liquid crystal display element.
On the other hand, a reflection type liquid crystal display device displays an image by using ambient light, and thus does not require a backlight. Therefore, a reflection type liquid crystal display device has a number of advantages such as a small weight, a small thickness, and a low power consumption. Moreover, the visibility does not lower even under very bright environments, and a displayed image can be viewed more clearly under bright environments. However, with a reflection type liquid crystal display device, the display brightness and the contrast ratio are substantially influenced by the conditions under which it is used, e.g., the brightness of the environment. Particularly, the visibility lowers significantly under dark environments.
Therefore, some reflection type liquid crystal display devices are provided with an illuminator for improving the display quality in cases where ambient light of a sufficient intensity is not available. The illuminator is provided on the front side of the liquid crystal display element, and is called “frontlight” as opposed to the illuminator of a transmission type liquid crystal display device being called “backlight”.
FIG. 7
schematically illustrates a reflection type liquid crystal display device
600
A, which is disclosed in “Monthly DISPLAY”, November 2001 issue (Techno Times Co., Ltd.), p. 56 to p. 62, “Frontlight Technical Trend”.
As illustrated in
FIG. 7
, the reflection type liquid crystal display device
600
A includes a reflection type liquid crystal display element
620
, and a front light
610
provided on the viewer side of the reflection type liquid crystal display element
620
.
The front light
610
includes a light source
611
and a light guide
613
, and a reflection film
612
is provided so as to surround the light source
611
.
The light guide
613
includes a light-receiving surface
613
a
for receiving light from the light source
611
, a light-exiting surface
613
b
provided so as to be substantially perpendicular to the light-receiving surface
613
a
, and a counter surface
613
c
opposing the light-exiting surface
613
b
. The reflection type liquid crystal display element
620
is provided on one side of the light guide
613
that is closer to the light-exiting surface
613
b
. The counter surface
613
c
includes a propagation surface
613
c
1
and a reflection surface
613
c
2
, and has a saw-toothed cross section.
Light emitted from the light source
611
enters the light guide
613
through the light-receiving surface
613
a
, and propagates therethrough while being totally reflected between the light-exiting surface
613
b
and the propagation surface
613
c
1
. A portion of the light, which is being propagated through the light guide
613
, is reflected by the reflection surface
613
c
2
and emitted toward the reflection type liquid crystal display element
620
through the light-exiting surface
613
b.
The reflection type liquid crystal display element
620
includes a pair of glass substrates
621
a
and
621
b
, and a liquid crystal layer
622
and a reflector
623
provided between the pair of glass substrates
621
a
and
621
b
. A polarizer
624
a
and a &lgr;/4 film
624
b
are provided on the glass substrate
621
a
on the viewer side (the side closer to the front light
610
).
In the reflection type liquid crystal display device
600
A, circularly-polarized light that has entered the liquid crystal layer
622
via the polarizer
624
a
and the &lgr;/4 film
624
b
passes through the liquid crystal layer
622
, is reflected by the reflector
623
, and passes again through the liquid crystal layer
622
. In this process, the amount of light is controlled as the polarization thereof is modulated by the liquid crystal layer
622
, thereby displaying an image.
Anti-reflection films
631
a
and
631
b
are provided, through a vapor deposition process, on the light-exiting surface
613
b
of the light guide
613
and the polarizer
624
a
of the reflection type liquid crystal display element
620
, respectively, for an anti-air-interface-reflection treatment. Therefore, the air-interface reflection is suppressed at the interface between the light-exiting surface
613
b
and the air, and at the interface between the polarizer
624
a
and the air, thereby suppressing a decrease in the contrast ratio due to light being reflected at the interfaces toward the viewer side.
Moreover, the article (“Monthly Display”, November 2001 issue (Techno Times Co., Ltd.), p. 56 to p. 62, “Frontlight Technical Trend”) also discloses a reflection type liquid crystal display device
600
B illustrated in FIG.
8
.
In the reflection type liquid crystal display device
600
B, the polarizer
624
a
and the &lgr;/4 film
624
b
are attached to the light-exiting surface
613
b
of the light guide
613
via the adhesive layer
631
, as illustrated in
FIG. 8
, and light exiting through the light-exiting surface
613
b
of the light guide
613
passes through the polarizer
624
a
and the &lgr;/4 film
624
b
via the adhesive layer
631
to become circularly-polarized light. The light reflected at the interface between the &lgr;/4 film
624
b
and the air, and at the interface between the glass substrate
621
a
on the viewer side of the reflection type liquid crystal display element
620
and the air, passes again through the &lgr;/4 film
624
b
and is then absorbed by the polarizer
624
a
, thereby suppressing a decrease in the contrast ratio due to the reflection of light at the interfaces.
Moreover, Japanese Laid-Open Patent Publication No. 11-149252 discloses a reflection type liquid crystal display device
600
C in which the light guide
613
and the reflection type liquid crystal display element
620
are attached to each other via the adhesive layer
631
, as illustrated in FIG.
9
.
In the reflection type liquid crystal display device
600
C, the light guide
613
and the reflection type liquid crystal display element
620
are attached to each other via an adhesive layer
632
, as illustrated in
FIG. 9
, there is no air-element interface between the light guide
613
and the reflection type liquid crystal display element
620
. Therefore, an unnecessary air-interface reflection does not occur, thereby realizing a display with a high contrast ratio.
However, an in-depth research by the present inventor has revealed that the reflection type liquid crystal display devices
600
A,
600
B and
600
C have the following problems.
First, as illustrated in
FIG. 7
, with the anti-air-interface-reflection treatment using anti-reflection films, the air-interface reflection cannot be suppressed sufficiently. For example, in a case where an interference film made of a transparent material is formed as an anti-reflect
Cariaso Alan
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Tsidulko Mark
LandOfFree
Display device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3302491