Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2001-10-22
2004-08-31
Dowling, William C. (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S031000, C349S005000
Reexamination Certificate
active
06783241
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection-type display device which can be applied to for example a projector device for projecting an optical image spatially modulated by a reflection-type liquid crystal panel onto a screen.
2. Description of the Related Art
In the related art, a projection-type display device has been proposed which is configured to use a reflection-type liquid crystal panel to generate a spatially modulated optical image and to project this optical image onto the screen so as to form a desired color image.
FIG. 1
is a view of the configuration of this type of projection-type display device.
In this projection-type display device
1
, a light source
2
is constituted by for example a discharge lamp
3
and a reflector
4
and emits white illumination light. A convex lens
5
converts the illumination light emitted from the light source
2
to a substantially parallel luminous flux and then emits it.
A color separation mirror
6
on the optical path of the illumination light emitted from this convex lens
5
reflects the illumination light having a predetermined wavelength and transmits the remaining illumination light therethrough. A color separation mirror
7
on the optical path of the illumination light reflected at this color separation mirror
6
reflects the illumination light having a predetermined wavelength and transmits the remaining illumination light therethrough. Due to this, the projection-type display device
1
separates the illumination light emitted from the light source
2
to red, blue, and green illumination light.
A lens
8
, a mirror
9
, and a lens
10
bend the optical path of the illumination light transmitted through the color separation mirror
6
to guide the light to a polarization beam splitter
11
. The polarization beam splitter
11
emits illumination light having a predetermined plane polarization in the illumination light striking from this lens
10
toward a reflection-type liquid crystal panel
12
and transmits the illumination light having a plane polarization orthogonal to this plane polarization. Further, the polarization beam splitter
11
transmits a predetermined polarization component in the optical image emitted after spatially modulating the illumination light at the reflection-type liquid crystal panel
12
and emits it to a color synthesizing prism
13
.
A polarization beam splitter
14
similarly emits the illumination light having a predetermined plane polarization in the illumination light reflected at the color separation mirror
7
toward the reflection-type liquid crystal panel
15
and transmits the illumination light having the plane polarization orthogonal to this plane polarization therethrough. Further, the polarization beam splitter
14
transmits a predetermined polarization component in the optical image emitted after spatially modulation of the illumination light at the reflection-type liquid crystal panel
15
therethrough and emits it to the color synthesizing prism
13
.
A polarization beam splitter
16
similarly emits the illumination light having a predetermined plane polarization in the illumination light reflected at the color separation mirror
7
toward the reflection-type liquid crystal panel
17
and transmits the illumination light having a plane polarization orthogonal to this plane polarization therethrough. Further, the polarization beam splitter
16
transmits a predetermined polarization component in the optical image emitted after spatially modulation of the illumination light at the reflection-type liquid crystal panel
17
therethrough and emits it to the color synthesizing prism
13
.
The reflection-type liquid crystal panels
12
,
15
, and
17
spatially modulate the illumination light according to color signals corresponding to the wavelengths of the incident illumination light by being driven by a not illustrated drive circuit and project optical images rotated in their plane polarizations with respect to the illumination light toward the polarization beam splitters
11
,
14
, and
16
.
The color synthesizing prism
13
combines the optical images incident from these polarization beam splitters
11
,
14
, and
16
and emits the result. A projection lens
19
projects the resultant optical image emitted from this color synthesizing prism
13
onto the screen
20
.
Due to this, the projection-type display device
1
enlarges and projects the images formed on the reflection-type liquid crystal panels
12
,
15
, and
17
onto the screen
20
to thus display the intended color image.
The polarization beam splitters
11
,
14
, and
16
used for this type of projection-type display device
1
, however, also reflect and emit several percent of the amount of light incident of the components of plane polarization which originally must be transmitted. In the projection-type display device
1
, therefore, the unrequired plane polarization components reflected at the polarization beam splitters
11
,
14
, and
16
in this way are returned from the reflection-type liquid crystal panels
12
,
15
, and
17
to the polarization beam splitters
11
,
14
, and
16
and projected onto the screen
20
via the color synthesizing prism
13
.
Further, unmodulated components which are never polarized, but are reflected are also contained also in the modulated light reflected at the reflection-type liquid crystal panels
12
,
15
, and
17
. In the projection-type display device
1
, such components are also projected onto the screen
20
via the color synthesizing prism
13
.
Due to this, the projection-type display device
1
suffers from the defect of the haze phenomenon where a portion which should be originally displayed black is displayed white, so there is a problem that the contrast of the display image is still insufficient by that amount in practical use and the quality of the display image is poor.
Below, this haze phenomenon will be further considered from the viewpoint of the structure of the polarization beam splitter.
When a black portion is displayed white and this haze phenomenon is manifested, the contrast cannot be sufficiently secured by that amount in the image displayed on the screen.
A polarization beam splitter is formed by adhering inclined facets of rectangular prisms to each other. The incident light is detected by a laminate of dielectric films at the inclined facets. Accordingly, in the transmitted light and the reflected light of the polarization beam splitter, originally the linear polarized light resulting from this detection must be emitted.
The glass material constituting this type of rectangular prism, however, has a birefringence property. Due to this, the reflected light and the transmitted light to be originally emitted by the linear polarization are emitted by elliptical polarization.
Namely, the reflected light and the transmitted light comes to contain light having a plane polarization orthogonal to the plane polarization originally aimed at. Further, the light incident due to linear polarization comes to be detected by elliptical polarization, therefore part of the light to be originally transmitted or reflected will be reflected or transmitted by that amount and emitted reverse to the former.
When viewing this from the standpoint of the optical images emitted toward the polarization beam splitters from the reflection-type liquid crystal panels, the reflection-type liquid crystal panels spatially modulate the incident light having the predetermined plane polarizations and reflect optical images as the synthesized light of p-polarization components and s-polarization components. The optical images emitted in this way originally must be separated into the p-polarization components and the s-polarization components by the polarization beam splitters and only the optical images of the p-polarization components projected onto the screen.
However, the optical images become elliptical polarized light due to the birefringence of the polarization beam splitters. As a result, part of the s-polariz
Miyawaki Tetsuyuki
Yamamoto Hideki
Bell Boyd & Lloyd LLC
Dowling William C.
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