Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-12-28
2001-10-09
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C349S018000, C349S097000, C349S119000
Reexamination Certificate
active
06300929
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a flat panel display device in which a passive display element such as a liquid crystal display element or the like is used and, more particularly, to an outer (ambient) light reflection type flat panel display device.
Since liquid crystal display devices (LCDs) are optically passive elements, the LCDs need illumination light sources for image display. One of the most important requirements for the LCDs is lower power consumption which primarily depends on such illumination light sources. In order to meet that requirement, reflection type and semi-transmission light type liquid crystal display devices (LCD) have been developed. Since the reflection type LCD uses outer (ambient) light as an illumination light source, its display screen becomes dark in some circumstances due to lack of illuminance. Thus, it does not work usefully in a dark place.
The semi-transmission light type LCD, on the other hand, is provided with an illumination light source and a semi-transmission light (half) mirror to reflect outer (ambient) light so that it can be used as a transmission type LCD in dark circumstances while as a reflection type LCD under sufficiently illuminated conditions. The semi-transmission light mirror in the latter, however, is 50% at maximum efficiency of outer light utilization. Its screen illuminance is significantly poor in comparison with that of the transmission type or even reflection type LCDs.
Improvement of such a technical difficulty has been recently attempted for a semi-transmission light type LCD in which a plurality of pin-holes for each pixel are provided in a reflection plate and micro-lenses are correspondingly provided for each pin hole. In this LCD, since outer (ambient) light beams reflected from the reflection plate except the pin-holes are utilized while light beams passing through the micro-lenses are collected as a light-transmission type LCD when a light source disposed at the rear of the LCD is operated, its optical efficiency becomes better. When, however, the outer light beams are utilized, an optical loss takes place at the pin-holes. As a result, this LCD is often used as the light-transmission type and its power consumption is not always saved. Further, it is necessary to additionally install the reflection plate in the device from its outside to avoid an otherwise complicated structure. The reflection plate of this kind causes a parallax effect that decreases display performance.
Still another reflection type LCD is also under development. This reflection type LCD includes a front illumination light source which consists of a light guide provided on the observer side and a linear light source provided on a side edge of the light guide. Conspicuous light reflection on the front surface of the LCD, however, causes unsatisfactory display dignity, e.g., poor contrast.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a flat panel display device with a novel structure to overcome such technical difficulties in conventional reflection type or semi-transmission light type liquid crystal display devices as set forth above.
Another object is to provide a flat panel display device with high optical efficiency.
A flat panel display device of the invention is characterized in such a structure that a first polarizer, a first retarder plate, a polarized light reflection layer, a second retardation plate, and a second polarizer are laminated in that order viewed from the observer side. The polarized light reflection layer made of cholesteric liquid crystals selectively reflects left-handed or right-handed circularly polarized light components selected from light incident on its primary surface on the front side, and transmits its remains (right-handed or left-handed circularly polarized light components).
As shown in
FIG. 2
, where the cholesteric liquid crystal in the polarized light reflection layer
18
has a left-handed (counterclockwise) helical structure, a left-handed circularly polarized component L
1
derived from natural (ambient) light Lf incident on the primary surface
18
f
reflects on the surface
18
f.
A right-handed circularly polarized component L
1
passes through the polarized light reflection layer
18
. Similarly, a left-handed circular polarized component L
2
′ from natural incident light Lb reflects on the primary surface
18
b.
A right-handed circularly polarized component L
1
′ with respect to its advancing direction passes through the polarized light reflection layer
18
. As mentioned above, the circularly polarized light component substantially reflects on the cholesteric liquid crystal when a rotating direction of the former is consistent with a helical direction of the latter while the reversed component passes through the latter. If the cholesteric liquid crystal layer is made thin, the circularly polarized component with the consistent rotating direction with the helical direction passes by 10% through the cholesteric liquid crystal layer and selectively reflects thereon by 90%.
In a flat panel display device of the present invention, when light is incident from an observation surface, a linearly polarized light component which oscillates along a polarization axis of a polarizer comes out and reaches to a variable retarder. The retarder consists of fixed and variable retarder layers. The former preferably delays a phase of a specific-direction oscillating component derived from incident light by &lgr;/4 (&lgr;: an incident light wavelength) with respect to a reference oscillating component which crosses at right angles the specific-direction oscillating component. The latter also preferably delays, in response to a supplied voltage, a phase of a specific-direction oscillating component derived from incident light by &lgr;/2 with respect to a reference oscillating component which crosses the specific-direction oscillating component at right angles.
A well known &lgr;/4 retardation plate, for instance, can be used as such a fixed retarder layer. The &lgr;/4 retardation plate has a delay axis which defines 45° in a predetermined direction with respect to the polarizer. The retardation plate transforms the linearly polarized component passing through the polarizer into a circularly polarized component with a specific rotation direction. When the phase axis of the retardation plate is disposed at 45° in the right-handed direction, an outgoing circularly polarized component becomes right-handed (clockwise). When, on the other hand, the phase axis of the retardation plate is disposed at 45° in the left-handed direction, an outgoing circularly polarized component becomes left-handed (counterclockwise).
A variable retarder may be a birefringence layer which is controlled by voltages to change incident light phases. A vertical alignment homogeneous (VA) liquid crystal layer, for instance, is used as such a variable retarder layer. The VA liquid crystal layer has a negative dielectric anisotropy. When a lower voltage (first voltage) than a threshold value is applied to the VA liquid crystal layer, i.e., the VA liquid crystal layer maintains its initial vertical alignment to the substrate, the incident light is not subject to a phase modulation and passes through the VA liquid crystal layer. Its circular polarization remains unchanged. When a higher voltage (second voltage) than a saturated voltage is applied to the VA liquid crystal layer of which molecules are horizontally aligned to the substrate, an oscillation component of the incident light in a specific direction is delayed by a &lgr;/2 phase with respect to the other component thereof in a cross-nichol direction with the specific direction. As a result, its circular polarization direction is reversed.
As set forth above, the variable retarder layer composed of the liquid crystal causes a &lgr;/2 relative phase delay between the two separate occasions when the first and second voltages are applied to the layer. In the case of the VA liquid crystal layer, for instance, the first voltage is def
Hisatake Yuzo
Nakamura Takashi
Hjerpe Richard
Intellectual Property Group
Kabushiki Kaisha Toshiba
Lesperance Jean
Pillsbury Winthrop LI
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