Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-05-14
2001-09-04
Hjerpe, Richard (Department: 2674)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S068000, C349S069000, C349S062000, C349S064000, C349S061000, C345S087000
Reexamination Certificate
active
06285422
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a display device, and specifically to a display device using a liquid crystal as variable transmission polarization axis means or polarizer. Particularly, the present invention relates to a so-called transflective liquid crystal display device functioning as a transmissive liquid crystal display device when a light source is turned on, and functioning as a reflective liquid crystal display device when the light source is turned off. Also the present invention relates to electronic apparatus comprising the display device as a display unit, such as a watch, an electronic handbook, a personal computer, and the like.
2. Description of Related Art
A conventional liquid crystal display device comprising a variable transmission polarization axis optical element
2605
in which the polarization axis of a liquid crystal is variable, such as a TN (Twisted Nematic) liquid crystal, STN (Super-Twisted Nematic) crystal, or the like, has a structure in which the variable transmission polarization axis optical element
2605
is sandwiched between two polarizers
2601
and
2606
, as shown in FIG.
26
. Therefore, the conventional liquid crystal display device has a low efficiency of light utilization, and particularly, a reflective type has a problem with dark display.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a display device using a polarization changing element with a display device which is capable of obtaining a bright display.
Also, in a conventional transflective reflective liquid crystal display device, an Al reflecting plate is formed thin, or an opening is provided, thereby decreasing a reflectance at the reflective display. Namely, in a transflective type, brightness at the reflective display is sacrificed.
Accordingly, another object of the present invention is to provide a transflective and bright reflective liquid crystal display device with bright reflective display comprising a light source provided on the back of a reflective liquid crystal display device so as to permit not only reflective display by external light, but also display by transmitted light from the light source provided on the back.
In the transflective reflective liquid crystal display device, when external light is incident on the display device with the light source turned on, the display is sometimes hard to see due to positive-negative reversal.
Accordingly, a further object of the present invention is to provide a display device in which the display is not hard to see in case of positive-negative reversal.
In accordance with the present invention, a display device comprises a polarization changing element having a variable transmission polarization axis, first and second polarized light separators, disposed on both sides of the polarization changing element, sandwiching thereof, and a light source disposed opposite to the polarization changing element with respect to the second polarized light separator, wherein the first polarized light separator transmits light incident on a first side of the first polarized light separator that is, a linearly polarized in a first predetermined direction but does not transmit light that is linearly polarized in a second direction different from the first predetermined direction. The first polarized light separator also transmits light incident on the second side of the first polarized light separator that is linearly polarized light in the first direction but does not transmit light that is linearly polarized light in the second direction. The second polarized light separator transmits light incident on a polarization changing elements side that is linearly polarized in a third predetermined direction is transmitted to a light source side, However, light that is linearly polarized in a fourth predetermined direction different from the third predetermined direction is reflected to the polarization changing element side. As for light incident on the light source side, linearly polarized light in the third predetermined direction is emitted to the polarization changing element side.
In this display device of the present invention, for light incident from the outside of the first polarized light separator, two display states, i.e., a first display state created by the light reflected from the second polarized light separator, and a second display state where the light transmitted through the second polarized light separator is absorbed by the light source side, are obtained according to the state of the transmission polarization axis of the polarization changing element, to operate the display device as a reflective display device. The first display state is a display state created by the light reflected from the second polarized light separator and thus produces a bright display.
For light from the light source, two display states, i.e., a third display state created by the light transmitted through the first polarized light separator, and a fourth display state where no light is transmitted through the first polarized light separator, are obtained according to the state of the transmission polarization axis of the polarization changing element, to obtain a transmissive display.
The second polarized light separator is preferably polarized light separator in which for light over substantially the entire wavelength range of the visible light region, of light incident on the polarization changing element side, a linearly polarized light component in the third predetermined direction is transmitted to the light source side, and a linearly polarized light component in the fourth predetermined direction different from the third predetermined direction is reflected to the polarization changing element side. For light incident on the light source side which is light over substantially the entire wavelength range of the visible light region, linearly polarized light in the third predetermined direction is emitted to the polarization changing element side.
As a result, the first to fourth display states are obtained for light over substantially the entire wavelength range of the visible light region, and a transparent or white display can be obtained in the first and third display states.
The second polarized light separator is preferably polarized light separator in which of light incident on the polarization changing element side, a linearly polarized light component in the third predetermined direction is transmitted as linearly polarized light in the third predetermined direction to an optical element side. The second polarized light means is preferably polarized light separator comprising films laminated in a plurality of layers in which the refractive indexes of the plurality of layers are the same between each adjacent layer in the third predetermined direction, and different in the fourth predetermined direction.
The first polarized light separator preferably comprises a polarizer.
The polarization changing element preferably comprises a liquid crystal panel, particularly a TN liquid crystal panel, an STN liquid crystal panel, an F-STN liquid crystal panel or an ECB liquid crystal panel. Specifically, the STN liquid crystal panel is an STN liquid crystal panel using a color compensation optical anisotropic material, such as an F-STN (Film compensated Super-Twisted Nematic) liquid crystal panel, or an STN liquid crystal panel using the double refraction of a liquid crystal without using a color compensation optical anisotropic material.
Preferably, reflection from the surface of the light source can be suppressed by darkening the surface color of the light source. Consequently, it is possible to decrease the quantity of the light transmitted through the optical element and returned by reflection from the light source, thereby suppressing a decrease in contrast.
Preferably, an optical element is further provided between the second polarized light separator and the light source, which absorbs light from the second polarized light separator side, and t
Maeda Tsuyoshi
Okumura Osamu
Hjerpe Richard
Nguyen Francis
Oliff & Berridge PLC.
Seiko Epson Corporation
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