Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2000-03-13
2002-06-04
Dowling, William (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S033000, C348S742000
Reexamination Certificate
active
06398363
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a projection-type display system, and particularly to a field sequential color projection display system.
2. Description of Prior Art
LCD projection systems demand high brightness, high accuracy, excellent image quality and low cost, as well as compact size.
In an LCD projection system, the light source has to be effectively used in order to provide high brightness, thus requiring the use of a P/S converter and micro-lens and so on. A reflective-type LCLV (liquid crystal light valve) can further improve the image brightness and accuracy. Smaller LCD panels facilitate reducing the volume of the optical engine. However, the optical design and the cost of the system tend to trade-off with quality. It is difficult to provide a good quality LCD projection system at a low cost.
The prior arts, such as the three-panel LCD system disclosed in U.S. Pat. No. 4,904,061 by Aruga and the three-panel projection data monitor disclosed in IBM J. Res. Develop. Vol. 42, No. 3/4, 1998, by R. L. Melcher et al., can provide high light efficiency and high accuracy. However, in order to reduce the volume of the optical engine of an LCD system and simplify the optical design, two-panel or one panel LCD systems have been used to replace three-panel system without degrading the image quality. For example, referring to
FIG. 1
, U.S. Pat. No. 5,517,340 of Doang et al. passes the light emitted from the light source
13
through the polarizing color filter
16
and the broadband polarizing beam-splitting prism
12
so that s-polarized and p-polarized R, G, B light beams are sequentially incident to two reflective-type LCLVs
10
through two neighboring surfaces of the prism. The light beams reflected by the LCLVs
10
are combined by the prism
12
to form a single light beam, which passes through the projection lenses
14
to present a full-color image.
The applicant has disclosed a two-panel reflective-type ferro-electric LCLV system in Taiwanese Patent Application entitled “Field Sequential Dichroic Light Valve”. Referring to
FIG. 2
, the system comprises: a first right-angle prism
20
for guiding the incident light beam; a second right-angle prism
24
for reflecting the light beam to the polarizing beam-splitting prism; a rotary disk
22
for disposing R, G, B color filters to respectively pass only R, G. B light beams; a spindle motor
23
for driving the rotation of the rotary disk
22
; a broadband polarizing beam-splitting device
26
for respectively transmitting and reflecting the p-polarized light and the s-polarized light of sequentially produced R, G, B light beams; two fast time response LCLVs
28
,
29
for receiving and reflecting the p-polarized light and the s-polarized light of the R, G, B light beams, respectively, so that the p-polarized light is converted to s-polarized light and the s-polarized light is converted to p-polarized light; and projection lenses
30
for projecting the light beam to a screen after the s-polarized light and the p-polarized light respectively reflected by the LCLV
28
and
29
are reflected and transmitted by polarizing beam-splitting device
26
. This system is characterized in that the color filters are disposed on the disk. Since the response time of the ferroelectric liquid crystal panel is one thousand times faster than that of a TN (twisted neumatic) type LCLV, the images of s-polarized light and p-polarized light can be simultaneously displayed on the screen. The energy of the light source is therefore effectively used.
Another two-panel system disclosed by ITRI uses a beam splitting device including a color wheel and dichroic mirrors to simplify the optical engine.
Since the response time of ferroelectric LCLV is very fast, using a single panel incorporating the use of a fast field sequential beam splitting/combining component can obtain full-color projection display. For the prior arts shown in FIG.
1
and
FIG. 2
, using a light source having a linear polarization can easily simplify the two-panel system to a single-panel projection display system. However, the mechanical behavior of the color disk deteriorates the stability of optical engine.
In U.S. Pat. No. 5,347,378, M. A. Handschy et al. disclose a display device as shown in
FIG. 3
, in which a structure having serially arranged color selective ferroelectric liquid crystal components
40
performs fast time sequential switching, incorporating the use of a monochromatic display panel
32
to form a full-color display system. However, this device uses many polarizers
34
,
36
,
38
and
42
, which absorb a significant part of the light energy.
It is noted from the above description of the prior arts that it is desirable to combine a fast field sequential beam splitting/combining device, optical design with improved light efficiency, and a single panel fast response LCLV.
SUMMARY OF THE INVENTION
Accordingly, the object of this invention is to provide a field sequential color projection display system, which has high brightness, high accuracy and compact size, and is light and energy-saving.
To achieve the above object, this invention uses a fast response light valve, incorporating the beam splitting/combining theory of optical thin film to design a field sequential color projection display system including a single panel LCLV.
Compared with the conventional one-panel LCLV display system or the ferroelectric LCLV display system incorporating a color disk, the field sequential color projection display system of this invention can use the light energy more efficiently and has no drawback due to the mechanical behavior of the color disk.
Moreover, since the ferroelectric LCLV used in this invention has a diagonal dimension shorter than 1 inch and the prism module is compact, the volume of the optical engine is reduced relative to the prior art.
In the field sequential color projection display system of this invention, since the multi-layer thin film of the beam splitting/combining module is a polarizing mechanism, the system does not need to use a front polarizing device for the incident light beam. Thus, the optical engine is simplified and the volume of the system is reduced. Furthermore, the field sequential color projection display system of this invention has a structure good for mass production, providing a high utility for the relevant industry.
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patent: 5172221 (1992-12-01), Ko
patent: 5534949 (1996-07-01), Baron
patent: 5654775 (1997-08-01), Brennesholtz
patent: 5863125 (1999-01-01), Doany
patent: 5895109 (1999-04-01), Yamaguchi et al.
patent: 6113239 (2000-09-01), Sampsell et al.
patent: 6183091 (2001-02-01), Johnson et al.
patent: 6203160 (2001-03-01), Ho
patent: 6217174 (2001-04-01), Knox
patent: 6224216 (2001-05-01), Parker et al.
Ho Fang Chuan
Shen Wei
Yoo Jinn-Chou
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