Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2000-03-20
2002-07-16
Dowling, William (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S033000, C349S009000
Reexamination Certificate
active
06419362
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal projecting apparatus of three-panel type using three reflection-type light modulation elements such as a ferroelectric liquid crystal panel and, more particularly, relates to a miniaturization of a liquid crystal projecting apparatus.
An example of conventional liquid crystal projecting apparatuses using reflection-type liquid crystal panels will be shown in FIG.
5
.
As shown in
FIG. 5
, such a conventional liquid crystal projecting apparatus separating portion separates a white light emitted from a lamp
101
into RGB primary colors, using a dichroic mirror
102
for reflecting a red component light (hereinafter abbreviated as a red light), mirror
103
, and a dichroic mirror
104
for reflecting a green component light (hereinafter abbreviated as a green light).
The red light separated and reflected by the dichroic mirror
102
is incident on the major surface of a polarization beam splitter (hereinafter abbreviated as a PBS)
105
, then is reflected to the direction perpendicular to the incident light by a polarization separation surface which reflects a S-polarized component and incident on a reflection type liquid crystal panel
106
for red. The reflection type liquid crystal panel
106
for red rotates the polarization direction of the red light being incident on the pixels of the portion to be displayed in red by 90 degrees, that is, converts the red light into P-polarized light and reflects it. Thus, the P-polarized red light incident again into the PBS
105
transmits the polarization separation surface and is incident on the first major surface of a dichroic prism
111
for color combining.
The green and blue light transmitting the dichroic mirror
102
is reflected to the direction perpendicular to the incident light by a reflection mirror
103
and irradiated on a dichroic mirror
104
. The green light of the incident light is separated and reflected by the dichroic mirror
104
to the direction perpendicular to the incident light and incident on the major surface of the PBS
107
. Like the red light, the reflection type liquid crystal panel
108
for green converts the green light being incident on the pixels of the portion to be displayed in green into P-polarized light, then the green light is emitted from the direction perpendicular to the incident light and incident on the secondmajor surface of the dichroic prism
111
for color combining.
Further, like the red and green light, the reflection type liquid crystal panel
110
for blue converts the blue light transmits the dichroic mirror
104
and being incident on the pixels of the portion to be displayed in blue into P-polarized light, then the blue light is emitted from the direction perpendicular to the incident light and incident on the third major surface of the dichroic prism
111
for color combining.
When the image lights of the RGB primary colors are incident on the first to third major surfaces of the dichroic prism
111
for color combining, the image lights are color-combined on the dichroic surface, then the combined light is emitted from a projection optics
112
and so a color image is displayed on a not-shown screen.
However, since such a conventional liquid crystal projecting apparatus is arranged in a manner that the reflection type liquid crystal panel is disposed at each of the three PBSs for surrounding the three sides of the dichroic prism, the dichroic mirrors for color separation etc. are required to be disposed so as to detour the outside of the PBSs. As a result, there arises a problem that the size of the apparatus becomes large. In particular, when such a conventional liquid crystal projecting apparatus is used as a projection unit for a liquid crystal projecting apparatus of rear projection display, such an apparatus may not be housed within a narrow casing.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made in view of the aforesaid problems of the prior art, and an object of the present invention is to miniaturize a liquid crystal projecting apparatus.
The liquid crystal projecting apparatus according to the present invention comprises:
a light source portion for emitting light with predetermined polarization direction;
a color separating portion for separating the light emitted from the light source portion into a first separation light including a first color component of three primary colors and a second separation light including a second and a third color components having different polarization direction to each other, and for emitting the first and the second separation lights to different directions perpendicular to each other;
a first PBS disposed on the light emitting side of the first separation light of the color separating portion and having a first light modulating element of reflection type disposed on a major surface thereof on which the first separation light is incident;
a second PBS disposed on the light emitting side of the second separation light of the color separating portion, and having a second light modulating element of reflection type disposed on a major surface thereof on which the second color component of the second separation light is incident and having a third light modulating element of reflection type disposed on a major surface thereof on which the third color component of the second separation light is incident;
a color combining portion for combining the lights of the respective color components emitted from the first and the second PBSs; and
a projection optics for projecting the combined light combined by the color combining portion.
According to such an arrangement, the first separation light separated by the color separating portion is incident on the first PBS and modulated by the first light modulating element of reflection type. The modulated first separation light transmits the first PBS and is emitted to the direction perpendicular to the incident light and then incident on the color combining portion. The second separation light is incident on the second PBS and separated into a second and a third color components so as to be directed to different direction perpendicular to each other. The second and the third color components thus separated are modulated by the second and the third light modulating elements of reflection type, respectively, then combined by the second PBS, then emitted to the direction perpendicular to the incident light and incident on the color combining portion.
The first and the second separation lights combined by the color combining portion is projected on a screen by the projection optics thereby to display an image.
To be more concrete, the color separating portion is formed by a third PBS which has on the light source portion side a first polarization direction rotating portion for rotating polarization direction of the first color component by 90 degrees and has on the second PBS side a second polarization direction rotating portion for rotating polarization direction of the second color component by 90 degrees, and the color combining portion is formed by a fourth PBS which has on the second PBS side a third polarization direction rotating portion for rotating polarization direction of the second color component by 90 degrees.
Each of the color separating portion and the color combining portion is formed by a dichroic beam splitter which reflects the first color component and transmitting the second and third color components, and the color separating portion has on the second PBS side a fourth polarization direction rotating portion for rotating polarization direction of the second color component by 90 degrees.
Each of the polarization direction rotating portions is formed by a narrow band retarder corresponding to the color component which polarization direction is to be rotated.
Each of the light modulating elements of reflection type is formed by a ferroelectric liquid crystal panel.
REFERENCES:
patent: 5826959 (1998-10-01), Atsuchi
patent: 6176586 (2001-01-01), Hirose et al.
patent: 6183091 (2
Ikeda Takashi
Kanayama Hideyuki
Arent Fox Kintner Plotkin & Kahn
Dowling William
Sanyo Electric Co,. Ltd.
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