Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2000-02-17
2001-03-20
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S618000, C359S621000
Reexamination Certificate
active
06204972
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a projection-type display apparatus with a color light synthesizing device and an illumination optical system for the apparatus.
2. Description of Related Art
Projection-type display apparatuses for projecting a color image onto a projection screen employ a cross-dichroic prism in many cases. In a transmission-type liquid-crystal projector, a cross-dichroic prism is used as color synthesizing means for synthesizing three color light beams of red, green and blue and for outputting the synthesized light beam in the same direction. In a reflection-type liquid-crystal projector, a cross-dichroic prism is used as color separation means for separating a white light beam into three light beams of red, green and blue while being used as color synthesizing means at the same time for synthesizing back modulated three color light beams and outputting the synthesized light beam in the same direction. One of known projection-type display apparatuses using a cross-dichroic prism is disclosed in Japanese Unexamined Patent Publication 1-302385, for example.
FIG. 16
shows a concept of the major portion of a projection-type display apparatus. The projection-type display apparatus includes three liquid-crystal light valves
42
,
44
and
46
, a cross-dichroic prism
48
and a projection lens system
50
. The cross-dichroic prism
48
synthesizes three color light beams of red, green and blue respectively modulated by the three light valves
42
,
44
and
46
and outputs the synthesized light beam to the projection lens system
50
. The projection lens system
50
projects the synthesized light beam onto a projection screen
52
.
FIG. 17
is a partly exploded perspective view showing the cross-dichroic prism
48
. The cross-dichroic prism
48
is manufactured by gluing four right-angle prisms with right-angle surfaces interfaced by an optical cement.
FIGS.
18
(A) and
18
(B) are explanatory views illustrating the problem that arises when the cross-dichroic prism
48
is used. As shown in FIG.
18
(A), the cross-dichroic prism
48
has a red-color light reflecting film
60
R and a blue-color light reflecting film
60
B, both of which are arranged in the shape of the letter X at the interfaces formed in the right-angle surfaces of the four right-angle prisms. Since an optical cement layer
62
is formed in the gaps between four right-angle prisms, both the reflecting films
60
R and
60
B have a gap at the central axis
48
a
of the cross-dichroic prism
48
.
When a light beam passing through the central axis
48
a
of the cross-dichroic prism
48
is projected onto the projection screen
52
, a dark line resulting from the central axis
48
a
is displayed in a presented image. FIG.
18
(B) shows one example of such a dark line DL. The dark line DL, of a color different from the rest of the image, presents a slightly darker band at the center of the projected image. It is considered that the dark line DL is attributed to light scattering taking place in the gap in the central axis
48
a
and failure in the reflection of red-color light and blue-color light. This problem is also encountered in a cross-dichroic mirror in which two types of dichroic mirrors having selectively reflecting films, such as a red-color light reflecting film and a blue-color light reflecting film, are crossed in the letter X configuration. In this case, a dark line attributed to a central axis of the mirrors is also formed in a resulting image.
As described above, the dark line is created at the center of the screen by the central axis of the cross-dichroic prism
48
or the cross-dichroic mirror in the conventional projection-type display apparatus.
SUMMARY OF THE INVENTION
This invention has been developed with a view to resolving the above problem, and it is an object of the present invention to provide a technique that makes less pronounced a dark line attributed to a central axis of optical means having dichroic films of two types arranged in the letter X configuration, such as a cross-dichroic prism and a cross-dichroic mirror.
Referring to
FIGS. 1 through 4
, the principle for solving the problem is specifically discussed. Throughout the drawings, a z direction is aligned with the direction of travel of the light beam, an x direction is at 3 o'clock position about the direction of travel of the light beam (z axis), and a y direction is at 12 o'clock position. See FIG.
2
. For convenience of the following discussion, the x direction represents the direction of rows and the y direction represents the direction of columns. Although the discussion of the principle is based on a specific example for simplicity, the present invention is not limited to such a specific example.
In the field of projection-type display apparatus, illumination optical systems (also referred to as an integrator optical system) having two lens arrays, each having a plurality of small lenses, as described in WO94/22042, are known as a technique for reducing nonuniform illuminance of an illuminating light by splitting a light beam into a plurality of partial light beams.
FIGS.
1
(A),
1
(B),
1
(C) and
1
(D) illustrates the principle of dark line generation in the projection-type display apparatus using a cross-dichroic prism which employs an integrator optical system. FIGS.
1
(A) and
1
(C) show light beams (represented by full lines) that are transmitted through small lenses
10
which are arranged in mutually different positions in the x direction, namely, small lenses
10
which are arranged in different positions in the direction of columns, and also show the trajectories (represented by thin broken lines) of central optical axes of the light beams. FIGS.
1
(B) and
1
(D) also show the positions of dark lines DLa and DLb on a screen
7
.
The light beam emitted by a light source (not shown) is split into a plurality of partial beams through a first lens array
1
and a second lens array
2
, each having a plurality of small lenses
10
. The light beams transmitted through the small lenses
10
in the first and second lens arrays
1
and
2
are converted into parallel light beams in parallel with the central axis of a collimator lens
15
. Partial light beams transmitted through the collimator lens
15
are superimposed on a liquid-crystal light valve
3
to illuminate uniformly a predetermined area. Although
FIG. 1
shows a single liquid-crystal light valve
3
only, the same principle of the integrator optical system and generation of dark line are true of the other two liquid-crystal light valves in a system such as illustrated in FIG.
18
(A).
FIG. 2
is a perspective view showing the external appearance of the first and second lens arrays
1
,
2
. Each of the first and second lens arrays
1
and
2
is constructed of a matrix of M rows and N columns of small lenses
10
, each having a rectangular shape. In this example, M=10 and N=8, and FIG.
1
(A) shows the trajectory of a partial light beam transmitted through a small lens
10
in the second column and FIG.
1
(C) shows the trajectory of a partial light beam transmitted through a small lens
10
in the seventh column.
Light beams superimposed on the liquid-crystal light valve
3
are modulated according to image information, and then directed to the cross-dichroic prism
4
. The light beam output from the cross-dichroic prism
4
is projected onto the screen
7
through a projection lens system
6
.
A light beam passing through the portion of the central axis
5
(along the y direction) is also projected at the positions of Pa and Pb on the screen
7
as represented by heavy broken lines in FIGS.
1
(A) and
1
(C). As already described in connection with the conventional art, light scattering takes place or a light, which would be otherwise reflected, is not reflected, in the gap between the reflecting films in the vicinity of the central axis
5
, and the quantity of light passing through in and around the central axis
5
is reduced. Referring to FIGS.
1
(B) and
1
(
Mack Ricky
Oliff & Berridg,e PLC
Seiko Epson Corporation
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