Liquid crystal cells – elements and systems – Liquid crystal system – Projector including liquid crystal cell
Reexamination Certificate
2000-01-21
2001-07-17
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Projector including liquid crystal cell
C349S113000, C349S003000, C353S020000, C359S490020
Reexamination Certificate
active
06262782
ABSTRACT:
BACKGROUNDS OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflective liquid crystal display and, more particularly, to a reflective liquid crystal display which can enhance light efficiency.
2. Description of the Prior Art
Generally, a liquid crystal display (“LCD”) is classified into a transmissive type and a reflective type: the former uses a backlight for radiating light frontward, while the latter uses a reflective film disposed on a rear side of the LCD to reflect light transmitted from a front side.
FIG. 4
shows a sectional view of a conventional reflective LCD.
A conventional LCD comprises upper and lower substrates
2
A and
2
B facing each other, ITO electrodes
4
A and
4
B formed on opposing inner surfaces of the upper and lower substrates
2
A and
2
B, respectively, and a liquid crystal layer
6
disposed between the upper and lower substrates
2
A and
2
B.
Attached on outer surfaces of the upper and lower substrates
2
A and
2
B are a polarizer
8
and a reflective layer
10
, respectively.
In addition, a red R, green G and blue B color filter with a black matrix BM may further provided to realize a color display.
In the operation of the LCD, when electric field is generated between the upper and lower ITO electrodes
4
A and
4
B by applying driving signals, the orientation of liquid crystal molecules in the liquid crystal layer
6
changes in accordance with a direction of the electric field to selectively transmit light.
Describing the transmission of the light, outer incident light is changed from circular polarization into linear polarization while passing through the polarizer
8
, and the linear polarization is changed into elliptical polarization while passing through the liquid crystal layer
6
via the upper substrate
2
A, the RGB color filter, and the ITO electrode
4
A. Then, the elliptical polarization passes through the ITO electrode
4
B and the lower substrate
2
B, then is reflected on the reflect layer
10
.
The reflected light is projected through the polarizer
8
in reverse order of the light incident course, thereby displaying an image.
FIG. 5
shows a schematic diagram for illustrating changes in an amount of light passing through the elements of the conventional LCD.
When outer light is introduced into the polarizer
8
, 50% of the light (“S-wave”) is absorbed and disappeared by the polarizer, and 50% of the light (“P-wave”) is transmitted to the reflective layer
10
via the liquid crystal layer
6
, then reflected thereon to be projected to the outside.
That is, 50% of the light is disappeared in the polarizer
8
. Therefore, the light efficiency of the LCD becomes about 50%. Light wave indicated by P′ in the drawing is the P-wave directed to the outside.
As described above, since the light efficiency is low, the image to be displayed is not clear. Therefore, many methods have been proposed to solve the above-described problems.
One of the methods is to use a high transmissive polarizer, which is sold in the trademark of DEBF polarizer by 3M Company.
However, even if the high transmissive polarizer is used, there is limitation in improving the light efficiency.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made in an effort to solve the above-described problem of the prior art.
It is an objective of the present invention to provide an LCD which can provide a high light efficiency by reducing an amount of light which is disappeared in a polarizer.
To achieve the above objective, the present invention provides a reflective LCD comprises first and second substrates facing each other, a liquid crystal layer disposed between the upper and lower substrates, a high transmissive polarizer attached on an outer surface of the first substrate, the high transmissive polarizer allowing a part of incident light to pass and reflecting the rest of the incident light, and an optical system disposed on the high transmissive polarizer, the optical system transmitting the reflected light to the high transmissive polarizer after changing an advancing direction of the reflected light to a polarizing direction such that the reflected light can be transmitted through the high transmissive polarizer.
According to a preferred example of the present invention, the optical system comprises an optical plate for transmitting light, which is reflected from the high transmissive polarizer, to a side wall thereof and for transmitting again the light transmitted from the side wall to the high transmissive polarizer, a retardation plate attached on the side wall of the optical plate to allow for &lgr;/4 phase retardation of the light transmitted from the optical plate, and an optical reflecting plate attached on the retardation plate.
REFERENCES:
patent: 5587816 (1996-12-01), Gunjima et al.
patent: 5712694 (1998-01-01), Taira et al.
patent: 5898521 (1999-04-01), Okada
Park Hong-Sik
Yamazaki Tsuneo
Baker & McKenzie
Samsung SDI & Co., Ltd.
Ton Toan
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