Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
1998-12-15
2001-01-30
Metjahic, Safet (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S034000
Reexamination Certificate
active
06179423
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a projection-type image display system which performs image display, by magnifying and projecting an image formed by an image display element, with the use of a projection lens or the like.
BACKGROUND OF THE INVENTION
A projection-type image display system magnifies and projects an image displayed on an image display element through a projection optical system, by utilizing the image display element as an optical switching element. Examples used as such image display elements include a transmission-type image display element which transmits and projects light, and a reflection-type image display element which reflects and projects light.
In a projection-type image display system using a transmission-type image display element, (1) a path of an illuminating light directed to the image display element, and (2) a path through which a light transmitted through and modulated by the image display element is projected through a projection lens onto a screen, are provided in different regions, respectively. On the other hand, in a projection-type image display system using a reflection-type image display element, parts or wholes of (1) a path of an illuminating light and (2) a path of a reflected light which has been modulated by the image display element are provided in the same region. Therefore, the projection-type image display system using the reflection-type image display element occupies a smaller space.
Further, in the transmission-type image display system, generally each pixel is equipped with a driving transistor. To prevent transistor characteristics from varying due to projection of light on the driving transistors, light blocking layers are laid on the driving transistors and signal lines to the pixels. The light blocking layers unavoidably make a numerical aperture of the pixels smaller. On the other hand, in the reflection-type image display element, generally the reflection surfaces serve as the light blocking layers, resulting in that the numerical aperture of the pixels is greater than that of the transmission type.
As a projection-type image display system using a reflection-type image display element, the Japanese Publication for Laid-Open Patent Application No. 63-39294/1988 (Tokukaisho 63-39294) discloses a video projection device having an optical system which decomposites/composites light from a light source by polarizing the same. Further, for example, the Japanese Publication for Laid-Open Patent Application No. 4-194921/1992 (Tokukaihei 4-194921) discloses a projection-type liquid crystal display (LCD) system using a polymer-diffusion-type liquid crystal, which modulates intensity of illuminating light by varying diffusion of reflected light, while the Japanese Publication for Laid-Open Patent Application No. 7-128664/1995 (Tokukaihei 7-128664) discloses a liquid crystal projector having a substantially identical structure to that of the foregoing projection-type LCD device.
First of all, a video projection device disclosed by Tokukaisho 63-39294 will be explained below.
FIG. 13
is a schematic view illustrating an arrangement of the video projection device. The video projection device is equipped with a light source
21
, a collimator lens
22
which collimates light from the light source, a polarizing beam splitter (hereinafter referred to as PBS)
23
, a color decompositing prism
24
, LCD elements
25
,
26
, and
27
which display blue, red, and green image components, respectively, reflection mirrors
28
,
29
, and
30
mounted on the LCD elements
25
,
26
, and
27
, respectively, and a projection lens
32
.
Light emitted from the light source
21
goes through the collimator lens
22
, thereby becoming a substantially parallel light, and enters the PBS
23
, where the light is split into linearly polarized light components directed in two directions orthogonal to each other. The light reflected by the PBS
23
out of lights obtained by splitting enters the color decompositing prism
24
.
The color decompositing prism
24
is composed of a first prism
24
A, a second prism
24
B, and a third prism
24
C. The light incident on the color decompositing prism
24
first enters the first prism
24
A, where a blue component is separated by a dichroic interference thin film and is guided to the LCD element
25
for displaying an image of the blue component. The light other than the blue component is incident on the second prism
24
B, where a red component is separated by a dichroic interference thin film and is guided to the LCD element
26
for displaying an image of the red component. The rest green component light is incident on the third prism
24
C, and is incident on the LCD element
27
for displaying an image of the green component.
The respective color component lights incident on the LCD elements
25
,
26
, and
27
are reflected by the reflection mirrors
28
,
29
, and
30
, respectively, and go through the LCD elements
25
,
26
, and
27
again, respectively. Here, the color component lights going through the LCD elements
25
,
26
, and
27
are subject to modulation of polarization directions, in accordance with image signals of the LCD elements
25
,
26
, and
27
, respectively.
The color component lights subject to the modulation of polarization direction are again incident on the color decompositing prism
24
, where they are composed. The composed light is incident on the PBS
23
, and only the polarized components which are allowed to go through the PBS
23
, out of the light subject to the modulation of polarization direction, are projected onto a screen (not shown) by the projection lens
32
.
Next, the projection-type LCD device disclosed by Tokukaihei 4-194912 will be explained below.
FIG. 14
is a schematic view illustrating an arrangement of the projection-type LCD device. The projection-type LCD device is equipped with a light source section including a light source
41
and a paraboloidal mirror
42
, a lens
43
for converging light from the light source section, a cross dichroic prism
44
, reflection/diffusion-type LCD devices
45
R,
45
G, and
45
B for displaying images of red, green, and blue color components, respectively, a convergence lens
46
, first and second blocking masks
47
and
48
, a reflection mirror
49
, a projection lens
50
, and a screen
51
.
White light emitted from the light source section is converged by the lens
43
, and reflected by the reflection mirror
49
. Thereafter, the white light goes through the convergence lens
46
, thereby being converted to a substantially parallel light, and is incident on the cross dichroic prism
44
.
The white light incident on the cross dichroic prism
44
is decomposited into red, green, and blue color components, and the color components are reflected by the reflection/diffusion-type LCD devices
45
R,
45
G, and
45
B, respectively. Here, degrees of diffusion of the lights of the respective color components upon reflection are varied in accordance with image signals of the reflection/diffusion-type LCD devices
45
R,
45
G, and
45
B, respectively.
The lights of the color components reflected by the reflection/diffusion-type LCD devices
45
R,
45
G, and
45
B are composited by the cross dichroic prism
44
, and the composited light enters the convergence lens
46
. The light entering the convergence lens
46
is converged to the vicinity of an aperture surrounded by an end of the first blocking mask
47
and an end of the reflection mirror
49
, and is projected onto the screen
51
through the projection lens
50
.
When the projection-type LCD device conducts black display, lights of the color components reflected by the reflection/diffusion-type LCD devices
45
R,
45
G, and
45
B become diffused lights. The diffused lights are hardly converged to the vicinity of the aperture by the convergence lens
46
, but are absorbed and blocked by the first and second blocking masks
47
and
48
, or alternatively, reflected by the reflection mirror
49
thereby returning to the light source section. As a r
Hamada Hiroshi
Kato Hiromi
Leroux E P
Metjahic Safet
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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