Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-04-28
2001-11-13
Malinowski, Walter J. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S098000
Reexamination Certificate
active
06317180
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transflective liquid crystal device (hereinafter also referred to as a transflective liquid crystal device) capable of both reflective display, which reflects incident light to display an image, and transmissive display, which transmits incident light to display an image.
2. Description of the Related Art
The transflective liquid crystal device is widely used as a display device of portable information equipment.
FIG. 11
schematically illustrates the structure of a conventional transflective liquid crystal device
1000
. The transflective liquid crystal device
1000
includes an absorptive polarizer
1020
, a liquid crystal cell
1030
, a light diffusing plate
1040
, a reflective polarizer
1050
, and a light absorbing plate
1060
. A backlight
1070
is further disposed outside the light absorbing plate
1060
. The liquid crystal cell
1030
includes a lower glass substrate
1033
, an upper glass substrate
1031
, and a liquid crystal layer
1035
sealed between these glass substrates
1031
and
1033
. A plurality of transparent signal electrodes
1034
are mounted on the upper surface of the lower glass substrate
1033
. A plurality of transparent scanning electrodes
1032
are mounted to be perpendicular to the plurality of signal electrodes
1034
on the lower surface of the upper glass substrate
1031
. The liquid crystal cell
1030
has a passive matrix configuration, in which one pixel is defined by one signal electrode
1034
, one scanning electrode
1032
, and the liquid crystal layer
1035
between these electrodes
1034
and
1032
. Namely the light transmitted through the liquid crystal layer
1035
is modulated according to the voltage applied between one signal electrode
1034
and one scanning electrode
1032
. The liquid crystal layer
1035
may be made of a TN (twisted nematic) liquid crystal composition or STN (super twisted nematic) liquid crystal composition. A translucent film having the transmittance of about
50
% is used for the light absorbing plate
1060
.
FIG. 12
shows problems arising in the conventional transflective liquid crystal device
1000
. The absorptive polarizer
1020
has an axis of transmission
1020
T that is set parallel to the plane of the drawing, and an axis of absorption
1020
A that is perpendicular to the plane of the drawing. The reflective polarizer
1050
has, on the other hand, an axis of transmission
1050
T that is parallel to the plane of the drawing, and an axis of reflection
1050
R that is perpendicular to the plane of the drawing. The following describes the operations of the liquid crystal display
1000
on the assumption that the polarizing direction of the light transmitted through the liquid crystal cell
1030
is rotated by 90 degrees while no voltage is applied between the signal electrodes
1034
and the scanning electrodes
1032
(that is, when the liquid crystal cell
1030
is in an OFF state).
This liquid crystal device
1000
has two display modes, that is, a reflective display mode using incident light
1100
from the outside and a transmissive display mode using light
1120
emitted from the backlight
1070
. In the reflective display mode, when the non-polarized light
1100
enters the absorptive polarizer
1020
, a linearly polarized light component having the polarization direction parallel to the axis of absorption
1020
A is mostly absorbed by the absorptive polarizer
1020
, while only a linearly polarized light component having the polarization direction parallel to the axis of transmission
1020
T is transmitted through the absorptive polarizer
1020
and enters the liquid crystal cell
1030
. The optical rotatory power of the liquid crystal cell
1030
causes the light component entering the liquid crystal cell
1030
to be converted into linearly polarized light having a polarizing direction that is perpendicular to that of the incident light. The polarizing direction of the light emitted from the liquid crystal cell
1030
is substantially identical with the direction of the axis of reflection
105
OR of the reflective polarizer
1050
, so that most of the light emitted from the liquid crystal cell
1030
is reflected by the reflective polarizer
1050
and re-enters the liquid crystal cell
1030
as return light. The liquid crystal cell
1030
converts the return light into linearly polarized light having a polarizing direction that is perpendicular to that of the return light. At this moment, the polarizing direction of the return light emitted from the liquid crystal cell
1030
is substantially identical with the direction of the axis of transmission
1020
T of the absorptive polarizer
1020
, so that most of the return light emitted from the liquid crystal cell
1030
is transmitted through the absorptive polarizer
1020
. In the reflective display mode, the pixels where the liquid crystal cell
1030
is in the OFF state receive the light reflected and returned as discussed above and are thereby observed as bright pixels. The pixels where the liquid crystal cell
1030
is in an ON state are, on the contrary, observed as dark pixels.
In the transmissive display mode, on the other hand, when the non-polarized light
1120
enters the reflective polarizer
1050
, a linearly polarized light component having the polarization direction parallel to the axis of reflection
105
OR is mostly reflected by the reflective polarizer
1050
, while only a linearly polarized light component having the polarization direction parallel to the axis of transmission
1050
T is transmitted through the reflective polarizer
1050
and enters the liquid crystal cell
1030
. The optical rotatory power of the liquid crystal cell
1030
causes polarizing direction of the light transmitted through the liquid crystal cell
1030
to be converted into a direction substantially parallel to the axis of absorption
1020
A of the absorptive polarizer
1020
. Most of the light emitted from the liquid crystal cell
1030
is accordingly absorbed by the absorptive polarizer
1020
and is not transmitted through the absorptive polarizer
1020
. In the transmissive display mode, since the light is absorbed in the course of the optical path, the pixels where the liquid crystal cell
1030
is in the OFF state are observed as dark pixels. The pixels where the liquid crystal cell
1030
is in the ON state are, on the contrary observed as bright pixels. The relationship between the ON/OFF state of the liquid crystal cell
1030
and the bright/dark state of the pixel in the transmissive display mode is reverse to that in the reflective display mode. In the transflective liquid crystal device
1000
, the brightness and darkness of display are reversed between the reflective display mode and the transmissive display mode.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide a liquid crystal device that effectively prevents the reversion of the same bright/dark states between the reflective display mode and the transmissive display mode, and also to provide an electronic apparatus using such a liquid crystal device.
At least part of the above and the other related objects is attained by a liquid crystal device that modulates light responsive to given image signals. The liquid crystal device includes a first absorptive polarizer, which receives light from outside;a liquid crystal cell, which receives light emitted from the first absorptive polarizer; a second absorptive polarizer, which receives light emitted from the liquid crystal cell; and a reflective polarizer, which receives light emitted from the second absorptive polarizer. The reflective polarizer has an axis of reflection in a predetermined direction to reflect at least part of light that has been transmitted through the first absorptive polarizer, the liquid crystal cell, and the second absorptive polarizer to be incident on the reflective polarizer. The reflective polarizer partially transmits light including a linearly polarized light component which is included
Kuroiwa Masahiro
Miwa Naonori
Tsuda Atsunari
Malinowski Walter J.
Seiko Epson Corporation
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