Optics: image projectors – Color filter
Reexamination Certificate
2001-02-16
2003-05-27
Mathews, Alan A. (Department: 2851)
Optics: image projectors
Color filter
C353S031000
Reexamination Certificate
active
06568815
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a picture projection apparatus for projecting a picture displayed by spatial modulation means employing e.g., a liquid crystal panel.
2. Description of Related Art
Such picture projection apparatus is comprised of three liquid crystal panels
101
a,
101
b,
101
c,
as transmission type spatial modulation means, as shown in FIG.
1
. In this picture projection apparatus, a light beam radiated from a light source
102
, such as a halogen lamp, falls on a polarized light conversion system
104
, through an integrator
103
, to become a unidirectional linear-polarized light beam. The polarized light conversion system
104
includes a large number of polarized light beam splitters, a mirror and a ½ wavelength plate arranged in association with these polarized light beam splitters. In this polarized light conversion system
104
, the light beam transmitted through the respective polarized light beam splitters are P-polarized light beams relative to the reflective surfaces of the polarized light beam splitters. The light beam reflected by the polarized light beam splitters are transmitted through the ½ wavelength plate to prove P-polarized light beam with respect to the reflective surfaces of the polarized light beam splitters.
A light beam through the polarized light conversion system
104
is reflected through a first condenser lens
105
a
by a first mirror
106
a
to fall on a first dichroic mirror
107
a.
In the light beam incident on this first dichroic mirror
107
a,
a first prime color component is transmitted, whilst the second and third prime color components are reflected. The first prime color component, transmitted through the first dichroic mirror
107
a,
is reflected by a second mirror
106
a
to fall through a second condenser lens
105
b
on a first liquid crystal panel
101
a.
This first liquid crystal panel
101
a
displays an image corresponding to the first prime color component to modulate the transmitted light in keeping with this image.
The second and third prime color components, reflected from the first dichroic mirror
107
a,
are incident on a second dichroic mirror
107
b.
In the light beam, incident on the second dichroic mirror
107
b,
the second prime color component is reflected, whilst the third prime color component is transmitted. The second prime color component, reflected by the second dichroic mirror
107
b,
falls through a third condenser lens
105
c
on the second liquid crystal panel
101
b.
This second liquid crystal panel
101
b
displays an image corresponding to the second prime color component and modulates the transmitted light in keeping with this image.
The third prime color component, transmitted through the second dichroic mirror
107
b,
is transmitted through a fourth condenser lens
105
d,
a third mirror
106
c,
a fifth condenser lens
105
e,
a fourth mirror
106
d
and a sixth condenser lens
105
f
in this order to fall on the third liquid crystal panel
101
c.
The third liquid crystal panel
101
c
displays an image corresponding to the third prime color component and modulates the transmitted light in keeping with the displayed image.
The light beams, transmitted through the first to third liquid crystal panels
101
a
to
101
c,
are incident from three directions on and synthesized by a dichroic prism
109
to exit from this dichroic prism
109
. The light beam exiting from this dichroic prism
109
falls on a projection lens
110
so as to be projected on a screen, not shown. The light beam exiting from the dichroic prism
109
is synthesized from three prime color components, so that a color image is projected by a projection lens
110
.
A certain known image projection device is made up of three liquid crystal panels
111
a,
111
b,
111
c,
as reflection type spatial modulation means, as shown in FIG.
2
. In this image projection device, a light beam exiting from a light source
102
falls through an integrator
103
on the polarized light conversion system
104
to prove a unidirectional linear polarized light beam. The light beam transmitted through the polarized light conversion system
104
is reflected through the first condenser lens
105
a
by a mirror
106
so as to fall through the second condenser lens
105
b
on a polarizing beam splitter
112
.
The incident light beam on the polarizing beam splitter
112
is an S-polarized light relative to the reflective surface of the polarizing beam splitter
112
and is reflected on a reflecting surface to fall on a first dichroic prism
113
a.
In the light beam, incident on the first dichroic prism
113
a,
the first prime color component is reflected on the inner prism surface, while the second and third prime color components are transmitted. The first prime color component, reflected by the inner surface of the first dichroic prism
113
a,
falls on the first liquid crystal panel
111
a.
This first liquid crystal panel
111
a
displays an image corresponding to the first prime color component and modulates and reflects the incident light in keeping with the image.
The second and third prime color components, transmitted through the first dichroic prism
113
a,
fall on the second dichroic prism
113
b.
In the light beam incident on the second dichroic prism
113
b,
the second prime color component is reflected by the inner prism surface, while the third prime color component is transmitted. The second prime color component, reflected by the inner surface of the second dichroic prism
113
b,
falls on the second liquid crystal panel
111
b.
This second liquid crystal panel
111
b
displays an image corresponding to the second prime color component and modulates and reflects the incident light in keeping with the image.
The third prime color component, transmitted through the second dichroic prism
113
b,
falls through the prism
113
c
on the third liquid crystal panel
111
c.
This third liquid crystal panel
111
c
displays an image corresponding to the third prime color component and modulates and reflects the incident light in keeping with the image.
The light beam, reflected by the first to third liquid crystal panels
111
a
to
111
c,
are synthesized by inversely following an optical path comprising the liquid crystal panels
111
a,
111
b
and
111
c
to exit from the first dichroic prism
113
a
to fall on the polarizing bean splitter
112
. The incident light beam on the polarizing beam splitter
112
is the p-polarized light relative to the reflecting surface of the polarizing beam splitter
112
and is transmitted through the reflecting surface to fall on the projection lens
110
. The light beam exiting from the first dichroic prism
113
a
is synthesized from three prime color components, so that a color image is projected by a projection lens
110
.
The image projection device is made up of three liquid crystal panels in order to display images corresponding to the three prime colors of red (R), green (G) and blue (B).
The above-described image projection device has many optical components, especially if it is provided with a transmission type liquid crystal panel, and hence is complex to assemble and fabricate. Moreover, if the liquid crystal panel is of the transmission type, the aperture ratio is low because of the necessity of providing the wiring etc.
If the reflection type liquid crystal panel is used, it is possible to reduce the size and to increase the aperture ratio as compared to the case in which the transmission type liquid crystal panel is used. However, if the reflection type liquid crystal panel is used, the length between the liquid crystal panel and the projection lens is increased as compared to the case in which the transmission type liquid crystal panel is used, with the back focus of the projection lens being longer. So, a projected image with a sufficient luminosity cannot be realized except if the diameters of the projection lens and the polarizing beam splitter are increased.
SUMMARY OF THE INVENTION
It is therefor
Esplin D. Ben
Kananen, Esq. Ronald P.
Mathews Alan A.
Rader & Fishman & Grauer, PLLC
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