Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2000-12-29
2002-06-11
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S637000, C359S640000, C353S033000
Reexamination Certificate
active
06404558
ABSTRACT:
BACKGROUND
0
F THE INVENTION
1. Field of the Invention
The invention relates to a projection display, more particularly to a single-lens type projection display with a color separation/synthesizing prism unit.
2. Description of the Related Art
In a conventional projection display, white light is separated into first, second and third color components that are subsequently and respectively modulated by a corresponding light valve. The modulated color components are then synthesized to form an output beam prior to reception by a projection lens for projecting a color image on a display screen.
U.S. Pat. No. 5,644,432 discloses a three-prism color separator for use with three reflective light valves. As shown in
FIG. 1
, according to this patent, white light
10
from a polarizing cube
11
is separated into red, green and blue color components by an optical beam splitter
12
that includes first, second and third prisms
121
,
122
,
123
. The three color components are directed by the three prisms
121
,
122
,
123
to three reflective light valves
131
,
132
,
133
for light modulation. Thereafter, the light-modulated color components retrace their paths through the three prisms
121
,
122
,
123
so as to be synthesized to form an output beam that is to be received by a projection lens (not shown) via the polarizing cube
11
for projecting a color image.
FIG. 2
illustrates another conventional projection display
2
. The projection display
2
includes a light source
21
and a light filter
22
downstream of the light source
21
for removing ultra-violet rays and infra-red rays from a light beam generated by the light source
21
to obtain a white beam output. First and second beam splitters
231
,
232
split the white beam output from the light filter
22
into first, second and third color components
201
,
202
,
203
, such as red, green and blue color components. The first and second color components
201
,
202
from the second beam splitter
232
are modulated by first and second transmissive light valves
251
,
252
, respectively. The third color component
203
from the first beam splitter
231
is reflected by a mirror
241
prior to modulation by a third transmissive light valve
253
. After modulation, the three color components
201
,
202
,
203
are synthesized using two beam splitters
233
,
234
and a mirror
242
prior to reception by a projection lens
26
for projecting an image on a display screen (not shown). Particularly, the first color component
201
is reflected once by the mirror
242
before passing through the beam splitter
233
. The second color component
202
is reflected once by each of the beam splitters
234
,
233
. The third color component
203
passes through the beam splitter
234
before being reflected by the other beam splitter
233
.
Because the three color components
201
,
202
,
203
either pass through or are reflected by the beam splitters
234
,
233
and the mirror
242
in different ways during color synthesizing, minor differences inherent in the different optical paths can result in image distortion.
SUMMARY OF THE INVENTION
Therefore, the main object of the present invention is to provide a single-lens type projection display which utilizes a color separation/synthesizing prism unit to ensure uniformity of the optical path lengths for the different color components during color separation and color synthesizing to minimize the occurrence of image distortion.
Another object of the present invention is to provide a single-lens type projection display with a color separation/synthesizing prism unit and which has light modulators that use transmissive light valves.
According to this invention, a projection display comprises:
a light source for generating a beam output that contains first, second and third color components;
a color separation/synthesizing prism unit having a color separation part for separating the beam output from the light source into the first, second and third color components that exit the prism unit in three different directions;
first, second and third light modulator means, disposed adjacent to the prism unit, for modulating the first, second and third color components that exit from the color separation part of the prism unit;
the prism unit further having a color synthesizing part that receives the modulated first, second and third color components from the first, second and third light modulator means and that synthesizes the modulated first, second and third color components so as to form an output beam; and
a projection lens for receiving the output beam from the color synthesizing part of the prism unit, and for projecting a color image.
The first, second and third color components have equal optical path lengths measured from the light source to the respective one of the first, second and third light modulator means. The first, second and third color components further have equal optical path lengths measured from the respective one of the first, second and third light modulator means to the projection lens.
Preferably, the prism unit includes first, second and third prisms, and the first, second and third color components exit the color separation part of the prism unit at the first, second and third prisms, respectively.
In the preferred embodiment, the color synthesizing part is vertically disposed relative to the color separation part of the prism unit. Each of the first, second and third light modulator means includes a transmissive light valve, a first mirror for reflecting the respective one of the first, second and third color components from the color separation part of the prism unit vertically, and a second mirror spaced apart vertically from the first mirror. The light valve is disposed between the second mirror and the color synthesizing part of the prism unit. The second mirror reflects the respective one of the first, second and third color components from the first mirror to the light valve.
REFERENCES:
patent: 5644432 (1997-07-01), Doany
patent: 5798819 (1998-08-01), Hattori et al.
patent: 6144498 (2000-11-01), Bryars et al.
patent: 6227670 (2001-05-01), Numazaki et al.
patent: 6238051 (2001-05-01), Huang
Chan Sheng-Hsiung
Chuang Fu-Ming
Epps Georgia
Merchant & Gould P.C.
Prokia Technology Co., Ltd.
Seyrafi Sareed
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