Liquid crystal cells – elements and systems – Liquid crystal system – Projector including liquid crystal cell
Reexamination Certificate
1999-02-24
2001-10-16
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Projector including liquid crystal cell
C353S031000
Reexamination Certificate
active
06304302
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 87108197, filed May 26, 1998, the full disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electronic optical system, and more particularly to a light projection system suitable for a use in a liquid crystal display system (LCD) to display image.
2. Description of Related Art
Recently, a LCD device is widely used in TV, computer, monitor or other display system. Comparing with a conventional display apparatus with a picture tube, the LCD system is lighter and has a smaller dimension. It becomes a necessary part to display system, such as a notebook computer.
FIG. 1
is a structure diagram, illustrating a polarization light projection system used in a reflection-type color display board as disclosed by U.S. Pat. No. 5,530,489. In
FIG. 1
, a reading light source
100
can emit a white light. The white light is polarized by a polarization beam splitter (PBS)
102
and split into an S-state polarized beam and a P-state polarized beam, both which are also reflected so that both light polarized beams are deflected by 90 degrees. The S-state polarized beam forms the WS beam. The P-state polarized beam is converted into an S-polarization beam WS′ through a half-wave plate
106
. The WS and WS′ beams are incident to a polarization analyzer
108
and are deflected by 90 degrees again, in which the polarization analyzer
108
further ensures that the Ws and the WS′ beams are polarized into an S polarized state.
The WS and the WS′ beams enter a dichroic prism
110
, which deflects a blue light BS of the WS and WS′ beams by 90° and allows a red light RS and a green light GS to continuously transmit. The blue light BS passes a light path compensation plate
112
and enters a blue liquid crystal light valve (LCLV)
114
, which converts the blue light BS into a blue light BP with P-state polarization and reflect the blue light BP back to the dichroic prism
110
through the light path compensation plate
112
. The blue light BP is deflected to a projection lens
122
through the polarization analyzer
108
. The projection lens
122
project the blue light BP onto an image screen (not shown). For the red light RS and the green light GS, they continuously travel to a color filter prism
116
, which deflects the green light GS by 90° into a red LCLV
118
, and allows the red light RS to pass and reach a green LCLV
120
. The red LCLV
118
reflects the green light GS back and converts it into a green light GP with P-state polarization. Similarly, the green LCLV
120
reflects the red light GS back and converts it into a red light GP with P-state polarization. The red light RP and the green light GP are also deflected to the projection lens
122
and projected to the image screen like the blue light BG.
In this system shown in
FIG. 1
, the system includes two light splitters and several prisms, resulting in a large system dimension. This display system cannot be efficiently applied in a large displaying area and is not portable. Moreover, a poor focusing quality severely occurs due to a too large distance between the LCLVs and the projection lens. This further limits its applications.
Another system is disclosed by U.S. Pat. No. 5,153,752 to reduce the distance of the projection lens and the system dimension.
FIG. 2
is a structure diagram, illustrating a polarization light projection system used in a reflection-type color display board as disclosed by U.S. Pat. No. 5,153,752. In
FIG. 2
, a light source
200
can emit a white unpolarized light S+P, which enters a PBS
201
and is split into an S-state polarized beam S
1
and a P-state polarized beam P
2
. The S-state polarized beam S
1
is deflected by 90° and enters a dichroic prism set
204
, which includes several dichroic prisms
204
a,
204
b,
204
c,
and
204
d.
After passing the dichroic prism set
204
, the S-state polarized beam S
1
are split into a red light RS, a green light GS, and a blue light BS, which respectively travel to LCD panels
205
R,
205
G and
205
B. The LCD panels
205
R,
205
G and
205
B respectively convert the red light RS, the green light GS, and the blue light BS into a red light RP, a green light GP, and a blue light BP with P-state polarization, and reflect the lights RP, GP, and BP onto a projection lens
206
, which projects passing light onto a screen (not shown).
For the P-state polarized beam P
2
, as it passes the PBS
201
, it enters a half-wave plate
202
and is polarized to an S-state polarized beam S
2
. The S-state polarized beam S
2
, similar to the S-state polarized beam S
1
, is reflected by the LCD panels
205
R,
205
G and
205
G and reach the screen at the end.
In this conventional projection system of
FIG. 2
, the dimension and the light focusing issues of the conventional projection system of
FIG. 1
is reduced. However, since the system of
FIG. 2
is very complicate, production yield rate is low and fabrication cost is high. Moreover, since several prisms are used in the system, a little misalignment may cause a large error. Its requirement of alignment precision is much higher that a usual level.
SUMMARY OF THE INVENTION
It is at least an objective of the present invention to provide a LCD system, particularly suitable for a color LCD system. The LCD system includes a projection system with a denser layout so that system dimension and back focal length are effectively reduced. A light path needs no a complicate reflection set so that there is no need of high alignment precision. Fabrication cost is also effectively reduced.
In accordance with the foregoing and other objectives of the present invention, a projection system used in a LCD system is provided. The projection system includes a light source, a polarization set which further includes a double dove prism, a vertical prism and a half-wave plate, a polarization beam splitter (PBS), a dichroic prism, and a projection lens. The light source emits a white light, which enters the polarization set and is split into a P-state polarized blue light and a mixed light. The mixed light includes an S-state polarized red light and an S-state polarized green light. The PBS allows the P-state polarized blue light to transmit and enter onto a blue light LCD panel, and deflects the mixed light by 90°. The dichroic prism splits the S-state polarized red light and the S-state polarized green light of the mixed light, which respectively enter a red light LCD panel and a green light LCD panel. The projection lens collects lights from the red, green, blue LCD panels and project the lights onto a screen.
REFERENCES:
patent: 5575548 (1996-11-01), Lee
patent: 5729306 (1998-03-01), Miyake et al.
patent: 5812223 (1998-09-01), Noguchi
patent: 6010221 (2000-01-01), Maki et al.
patent: 6042234 (2000-03-01), Itoh
patent: 6130728 (2000-02-01), Tsujikawa et al.
Ho Fang-Chuan
Huang Junejei
Industrial Technology Research Institute
Thomas Kayden Horstemeyer & Risley LLP
Ton Toan
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