Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
1998-05-14
2001-06-12
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S096000, C349S098000
Reexamination Certificate
active
06246455
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to display devices and electronic devices mounting the display devices. In particular, the present invention relates to a reflection-type liquid crystal display device and an electronic device mounting the reflection-type liquid crystal display device.
2. Description of the Related Art
A typical conventional liquid crystal display device using a polarization-changing optical element, such as a twisted nematic (TN) liquid crystal or a super-twisted nematic (STN) liquid crystal, which rotates the polarization axis, has a configuration in which the polarization-changing optical element is sandwiched between two polarizers. It therefore has a low light efficiency and, in particular, is a reflection-type display device having a dark display.
For the purpose of displaying in the dark, a transflector is provided below the liquid crystal display device and light is illuminated from its lower side. The use of the transflector causes a considerable amount of shading of the incident light, resulting in a dark display.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a display device with a bright display, which uses a polarization-changing optical element.
First, the principle of the present invention will be described with reference to
FIGS. 1A
to
12
.
FIGS. 1A
,
1
B, and
1
C are cross-sectional views for illustrating the principle of the display device in accordance with the present invention, whereas
FIG. 1D
is a cross-sectional view of the principle of a display device for comparison.
FIGS. 3
to
12
are cross-sectional views of the principle of the display device in accordance with the present invention. The liquid crystal display device in these drawings is shown to illustrate the principle of the present invention, hence the present invention is, of course, not limited to the liquid crystal display device shown in these drawings.
Referring now to
FIG. 1D
, the liquid crystal display device for comparison uses a polarizer
135
as a polarized-light separator at the observing side of the liquid crystal display device (herein after referred to as an upper polarized-light separator). The polarizer
135
transmits plane-polarized light from a light source
110
parallel to the drawing towards the observation side but absorbs plane-polarized light perpendicular to the drawing, hence the display from a light source
190
is dark.
In contrast, in the display device in accordance with the present invention, as shown in
FIG. 1A
, a retardation film
141
is provided on a glass substrate
142
for holding a STN liquid crystal
143
to correct coloring generated in the STN liquid crystal
143
. Also, an upper polarized-light separator
130
is provided on the retardation film
141
.
The upper polarized-light separator
130
includes a (¼)&lgr; plate
132
and a cholesteric liquid crystal layer
134
. The cholesteric liquid crystal reflects circularly polarized light having the same wavelength as the pitch of the liquid crystal and the same rotation direction as the liquid crystal, and transmits other light. For example, using a levorotation cholesteric liquid crystal with a pitch of 5,000 angstroms for the cholesteric liquid crystal layer
134
, the element is obtained, which reflects left-handed circularly polarized light with a wavelength of 5,000 angstroms and transmits left-handed circularly polarized light with other wavelengths and right-handed circularly polarized light. Further, by using the levorotation cholesteric liquid crystal and by varying its pitch over the entire wavelength range of visible light in the cholesteric liquid crystal, the element is obtained, which reflects left-handed circularly polarized light over the entire white light region rather than monochrome light and transmits right-handed circularly polarized light.
In the upper polarized-light separator
130
composed of a combination of such cholesteric liquid crystal layer
134
and (¼)&lgr; plate
132
, plane-polarized light of a given first direction incident on the (¼)&lgr; plate
132
is converted to left-handed circularly polarized light by the (¼)&lgr; plate
132
, reflected by the cholesteric liquid crystal layer
134
, reconverted to the plane-polarized light of the given first direction by the (¼)&lgr; plate
132
, and emitted. Plane-polarized incident light of the second direction perpendicular to the first direction is converted to right-handed circularly polarized light by the (¼)&lgr; plate
132
, and passes through the cholesteric liquid crystal layer
134
. Light incident on the upper side of the cholesteric liquid crystal layer
134
is emitted towards the lower side of the (¼)&lgr; plate
132
as plane-polarized light of the second direction.
As described above, the upper polarized-light separator
130
composed of a combination of the cholesteric liquid crystal layer
134
and the (¼)&lgr; plate
132
functions as a polarized-light separating means. The polarized-light separating means transmits the plane-polarized light of the second direction among the light incident on the (¼)&lgr; plate
132
and reflects the plane-polarized light of the first direction perpendicular to the second direction. Further, for the light incident on the cholesteric liquid crystal layer
134
, it emits plane-polarized light of the second direction to the side of the (¼)&lgr; plate
132
. Polarized-light separating means having such a function, other than the polarized-light separator
130
which comprises a combination of the cholesteric liquid crystal layer and (¼)&lgr; plate
132
, include that using a multilayered film (U.S. Pat. No. 4,974,219), that separating the incident light into reflected polarized light and transmitted polarized light by means of Brewster's angle (SID 92 DIGEST, pp. 427 to 429), and that using holograms.
Again, referring to
FIG. 1A
, plane-polarized light
191
parallel to the drawing from the light source
190
is converted to right-handed circularly polarized light by the (¼)&lgr; plate
132
and passes through the cholesteric liquid crystal layer
134
towards the observation side. On the other hand, plane-polarized light
192
perpendicular to the drawing from the light source
190
is converted to left-handed circularly polarized light by the (¼)&lgr; plate
132
, is reflected by the cholesteric liquid crystal layer
134
, is incident on the (¼)&lgr; plate
132
again, is converted to plane-polarized light perpendicular to the drawing, and travels towards the interior of the liquid crystal display device. Since the interior of the liquid crystal display device includes various boundary faces having discrete refractive indices such as, the plane-polarized light perpendicular to the drawing is reflected at boundary faces having discrete refractive indices such as, for example, boundary faces between air and the retardation film
141
and between the retardation film
141
and the glass substrate
142
, and is emitted towards the observer through the upper polarized-light separator after repeated reflection in the liquid crystal display device. Thus a brighter display is achieved for the display using the light from the light source
190
in comparison with the case using a polarizer as the upper polarized-light separator.
Referring now to
FIG. 1B
, the upper polarized-light separator
130
is provided with a (¼)&lgr; plate
132
, a cholesteric liquid crystal layer
134
, and a (¼)&lgr; plate
136
.
In the upper polarized-light separator
130
including the (¼)&lgr; plates
132
and
136
with the cholesteric liquid crystal layer
134
therebetween, plane-polarized light of a given first direction incident on the (¼)&lgr; plate
132
is converted to left-handed circularly polarized light by the (¼)&lgr; plate
132
, reflected by the cholesteric liquid crystal layer
134
, reconverted to the plane-polarized light of the f
Iijima Chiyoaki
Tsuchihashi Toshihiko
Oliff & Berridg,e PLC
Parker Kenneth
Seiko Epson Corporation
LandOfFree
Display device with liquid crystal between reflective... 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 with liquid crystal between reflective..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Display device with liquid crystal between reflective... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2488292