Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2003-07-02
2004-11-16
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
C359S629000, C359S628000, C359S640000, C359S833000, C353S020000, C353S033000, C349S009000
Reexamination Certificate
active
06819497
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color separation and color synthesis optical system applied to a reflection type projection display apparatus, and particularly to a color separation and color synthesis optical system capable of suppressing shading occurred for a color image, which is projected onto a screen, due to a difference of thermal expansion coefficients between a wavelength-selective polarization converting plate and a polarization beam splitter, and suppressing a decrease in a contrast ratio owing to an interface reflection light beam of the wavelength selection polarization plate provided on the side where a color-synthesized light beam is emitted.
2. Description of the Related Arts
A projection type display apparatus for projecting a color image is the one which color-separates a white light beam emitted from a light source portion into three primary color light beams of R (red), G (green) and B (blue), guides these three primary color light beams to a spatial light modulators corresponding thereto, and color-synthesizes the three primary color light beams, which have been optically modulated by the spatial light modulators of the three primary colors in accordance with video signals, to project the synthesized color light beam onto a screen, thus allowing the screen to display a color image thereon.
The projection type display apparatus for projecting the color image as described above can be roughly divided into a transmission type projection display apparatus which employs a transmission type spatial light modulator and a reflection type projection display apparatus which employs a reflection type spatial light modulator.
The transmission type projection display apparatus employing the transmission type spatial light modulator can be easily downsized thanks to its relatively simple optical structure. However, the transmission type projection display apparatus has a drawback in its capability for a high resolution performance. On the other hand, though the reflection type projection display apparatus employing the reflection type spatial light modulator has an advantage in its capability for a high resolution performance, this apparatus can not be easily downsized because of its complicated optical structure.
Particularly, the reflection type projection display apparatus employing the reflection type spatial light modulator requires a polarization beam splitter for separating an incident light beam to be radiated onto the reflection type spatial light modulator and a reflected light beam modulated by the reflection type spatial light modulator. At this time, since two or more polarization beam splitters are ordinarily operated for one reflection type spatial light modulator in order to obtain a high contrast color image, this makes the optical structure of the reflection type projection display apparatus complicated.
With respect to such reflection type projection display apparatus employing the reflection type spatial light modulator, a color separation and color synthesis optical system which solves the problem on its optical structure has recently been disclosed with several structural styles by Colorlink Inc. in the United States. For example, refer to the following Non-patent Literature 1, and the following Patent Literature 2.
Non-patent Literature 1: “High Contrast Color Splitting Architecture Using Color Polarization Filters” SID 00DIGEST, 92-95(2000), Michael G. Robinson et al.,
Patent Literature 2: U.S. Pat. No. 6,183,091B1
FIG. 1
is a plan view illustrating an optical structure of a color separation and color synthesis optical system applied to a reflection type projection display apparatus that is a conventional example disclosed by Colorlink Inc.
FIG. 2
is a plan view illustrating an optical structure of a color separation and color synthesis optical system applied to a reflection type projection display apparatus that is another conventional example disclosed by Colorlink Inc.
The reflection type projection display apparatus
1
A that is the conventional example illustrated in
FIG. 1
is introduced by Colorlink Inc. in the above described Non-patent Literature 1 (“High Contrast Color Splitting Architecture Using Color Polarization Filters” SID 00DIGEST, 92-95(2000), Michael G. Robinson et al.).
The reflection type projection display apparatus, which is the conventional example, constituted of a light source portion
10
for emitting a white light beam; a color separation and color synthesis optical system
30
A, which color-separates the white light beam emitted from the light source portion
10
into three primary color light beams of R (red), G (green) and B (blue), guides the three primary color light beams into three spatial light modulators
20
R,
20
G and
20
B corresponding to R, G and B, and emits a color-synthesized light beam obtained by color-synthesizing the three primary color light beams after the three primary color light beams are optically modulated by the spatial light modulators
20
R,
20
G and
20
B depending on video signals; and a projection optical system
40
for projecting the color-synthesized light beam emitted from the color separation and color synthesis optical system
30
A.
To be more concrete, the foregoing light source portion
10
is constituted of a reflecting plane mirror
11
; a light source
12
using a metal halide lamp, a xenon lamp, a halogen lamp or the like for emitting the white light beam; and a first polarization plate
13
which is provided ahead of the light source
12
and has a transmission axis selected so as to transmit only an s-polarized light beam in the white color light beam therethrough.
Accordingly, when the white light beam from the light source
12
transmits through the first polarization plate
13
, Rs, Gs and Bs light beams of three primary colors corresponding to R, G and B are incident onto the color separation and color synthesis optical system
30
A provided between the light source portion
10
and the projection optical system
40
.
In the following descriptions, the Rs, Gs and Bs light beams of the three primary colors shall show s-polarized light beams respectively corresponding to R, G and B. On the other hand, Rp, Gp and Bp light beams of three primary colors to be described later shall show p-polarized light beams respectively corresponding to R, G and B. At this time, the p and s-polarized light beams are determined based on a relative relation between a plane of polarization of linear polarization and a polarization-splitting plane of a polarization beam splitter onto which the p and s-polarized light beams are incident. When a light beam is in parallel with a paper plane, this light beam is referred to as the p-polarized light beam, and a light beam perpendicular to the p-polarized light beam is referred to as the s-polarized light beam.
The three spatial light modulators
20
R,
20
G and
20
B corresponding to R, G and B use a reflection type liquid crystal panel and the like, and quarter wave plates
21
to
23
are integrally fitted to front planes of the three spatial light modulators (hereinafter, referred to as a reflection type liquid crystal panel)
20
R,
20
G and
20
B. At this time, the quarter wave plates
21
to
23
serve to increase a contrast ratio of images of the respective colors displayed on the reflection type liquid crystal panels
20
R,
20
G and
20
B.
The color separation and color synthesis optical system
30
A surrounded by the dotted lines in
FIG. 1
is constituted of first to fourth polarization beam splitters
31
to
34
each formed to a rectangular parallelepiped shape (including a regular hexahedron shape), each having approximately the same outside dimension; and first to fourth wavelength-selective polarization converting plates
35
to
38
.
Specifically, in the foregoing color separation and color synthesis optical system
30
A, first to fourth polarization beam splitters
31
to
34
are located between the light source portion
10
and the projection optical system
40
s
Akino Ryuuji
Ashihara Makoto
Kashiwagi Takayuki
Masuda Shogo
Suzuki Tetsuji
Berkowitz Marvin C.
Victor Company of Japan , Limited
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