Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2001-12-12
2004-03-02
Dowling, William (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S033000, C349S005000
Reexamination Certificate
active
06698893
ABSTRACT:
RELATED APPLICATION
This application is based on application No. 2000-378589 filed in Japan, the contents of which are hereby incorporated by reference.
FIELD OF THE INVENTION
This invention relates optical devices used for synthesizing multiple light components and for separating light into multiple light components. This invention also relates to projection display apparatuses and image capturing devices that include such an optical device.
DESCRIPTION OF THE PRIOR ART
In the field of optics, it is sometimes desirable to separate light into multiple light components or synthesize multiple light components to form a single ray of light. For example, image projectors are known that generate a light ray for each of a set of primary colors, such as red, green and blue, and then combine, using a color synthesizer, each of the primary color light rays into a single light ray for projection.
One type of known color synthesizer is a cross-dichroic prism that comprises four identical triangular prisms. The prisms are bonded together such that the cross-section of the bonded surfaces, which work as dichroic surfaces, have a letter X configuration. For this reason, cross-dichroic prisms are often referred to as “x-cubes”.
An example of a projection display apparatus that attains color synthesis using a cross-dichroic prism is disclosed in Japanese Patent Publication No. 8-16828. An optical system for this type of projection display apparatus, as shown in
FIG. 5
, comprises a light source
1
, lens arrays
2
a
and
2
b
, reflection mirrors
3
a
and
3
b
, a superimposing lens
4
, dichroic mirrors M
1
and M
2
, a relay optical system
5
, field lenses
6
R,
6
G and
6
B, transmission-type light valves
7
R,
7
G and
7
B, a cross-dichroic prism
15
, and a projection lens
9
(having an optical axis AX) as well as other miscellaneous components. The spatial energy distribution of the light from the light source
1
is made uniform by an integrator means comprising the two lens arrays
2
a
and
2
b
and a superimposing lens
4
. Between the two lens arrays
2
a
and
2
b
, the light path of the illuminating light is bent by the reflection mirror
3
a
. Where the light valves
7
R,
7
G and
7
B are composed of liquid crystal, a polarization conversion means (not shown) is located near the integrator means in order to improve the efficiency of the use of the light from the light source
1
.
The first and second dichroic mirrors M
1
and M
2
are color separating means that separate the illuminating light exiting the integrator means into red (R), green (G) and blue (B) light components. The R light component is reflected by the first dichroic mirror Ml, and, after it is reflected by the reflection mirror
3
b
, it passes through the field lens
6
R. The G and B light components, on the other hand, pass through the first dichroic mirror M
1
. The G light component is reflected by the second dichroic mirror M
2
and then passes through the field lens
6
G. The B light component passes through the second dichroic mirror M
2
and then passes through the relay optical system
5
comprising relay lenses
5
a
and
5
c
and reflection mirrors
5
b
and
5
d
as well as the field lens
6
B.
Each field lens
6
R,
6
G and
6
B has a power determined such that the light exiting the lens strikes the pupil of the projection lens
9
. The R, G and B light components that have respectively passed through the field lenses
6
R,
6
G and
6
B are modulated by the transmission-type light valves
7
R,
7
G and
7
B that are provided near the field lenses
6
R,
6
G and
6
B. The modulated R, G and B light components are chromatically synthesized by the cross-dichroic prism
15
, which comprises a color synthesizer, and are then projected onto a screen (not shown) by the projection lens
9
.
The cross-dichroic prism
15
that performs color synthesis of the R, G and B light components comprises four triangular prisms bonded to one another, as described above. The dichroic surfaces, the cross-sectional configuration of which forms a letter X, reflect only R and B light components and allow the G light component to pass through, resulting in color synthesis of the three colors. In the color synthesis, the R light component exiting the first light valve
7
R, for example, is reflected by the first dichroic surface comprising two surfaces
15
a
and
15
b
. The fact that one dichroic surface
15
a
or
15
b
is defined by two different triangular prisms contributes to reduced precision in the manufacture of the cross-dichroic prism
15
. For example, if the accuracy of bonding of the prisms is poor, one dichroic surface becomes defined by two surfaces
15
a
and
15
b
that are parallel to but offset from each other with the apex
15
d
of one of the prisms serving as a boundary, as shown in FIG.
6
. In addition, if the precision in the processing of individual triangular prisms is poor, one dichroic surface becomes defined by two surfaces
15
a
and
15
b
that create an angle (180±&sgr;)° when measured with the apex
15
d
as the center, &sgr; representing the angular deviation from flatness created by the two surfaces, as shown in FIG.
7
.
The same precision-reducing factors exist with the second dichroic surface that reflects the light exiting the third light valve
7
B, as with the first dichroic surfaces
15
a
and
15
b
. When the light exiting the first and third light valves
7
R and
7
B is reflected by the first and second dichroic surfaces having reduced precision, respectively, partial mismatch occurs in the synthesis of the projected images from the individual light valves
7
R,
7
G and
7
B. This mismatch cannot be adjusted by adjusting the positions of the light valves
7
R,
7
G and
7
B relative to one another. If a cross-dichroic prism
15
, including precision reducing factors caused during manufacture, is used for color synthesis as described above, limitation results in making the light valves
7
R,
7
G and
7
B compact and delicate, in particular, due to concerns regarding precision. Furthermore, because manufacture ensuring high precision is required, the price of the product will also increase.
Another type of known color synthesizer, as illustrated in FIG.
8
and disclosed in Japanese Patent No. 2505758, is a dichroic prism
16
. Color synthesizers such as dichroic prism
16
are often refered to as “philips-type” prisms. The dichroic prism
16
has an optical axis AX and comprises three prisms P
1
, P
2
and P
3
. The bonded surfaces of the first prism P
1
and the second prism P
2
define a first dichroic surface D
1
. In the third prism P
3
, the surface that opposes a prism surface T
1
of the second prism P
2
with a certain space therebetween comprises a second dichroic surface D
2
. The third prism P
3
also has a prism surface T
2
, the significance of which will be discussed below. If a dichroic prism
16
(in
FIG. 8
) is used instead of the cross-dichroic prism
15
in the projection display apparatus described above with reference to
FIG. 5
, an optical construction shown in
FIG. 9
results. In
FIG. 9
, identical or equivalent members to those in the projection display apparatus shown in
FIG. 5
are indicated using the same numbers and letters.
The R light component undergoes total reflection by the prism surface T
1
, is reflected by the first dichroic surface D
1
, and is then synthesized with the G light component. The chromatically synthesized R and G light components strike the second dichroic surface D
2
. The B light component undergoes total reflection by the prism surface T
2
, followed by reflection by the second dichroic surface D
2
, and is synthesized with the R and G light components. The R, G and B light components synthesized by the two dichroic surfaces D
1
and D
2
exit through the prism surface T
2
, and are projected by the projection lens
9
onto a screen (not shown).
The dichroic prism
16
shown in
FIG. 8
entails little reduction in precision during manufacturing because both of the first and second dichroic surfaces D
1
an
Inoue Kazuhiko
Takimoto Shunta
Dowling William
Minolta Co. , Ltd.
Sidley Austin Brown & Wood LLP
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