Television – Video display – Projection device
Reexamination Certificate
2000-03-01
2003-04-29
Kostak, Victor R. (Department: 2711)
Television
Video display
Projection device
C352S109000, C359S833000, C353S081000
Reexamination Certificate
active
06556256
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a projector that projects images to display the images, and to a prism used therein.
2. Description of Related Art
In a projector, modulated light is formed by using an electro-optic device, and this modulated light is projected to display an image. Generally speaking, an “electro-optic device” is a device for converting an electric signal representing image information to modulated light. As this electro-optic device, an optical modulator which modulates light by controlling the emitting direction of illumination light applied to each pixel according to image information or the like is used. An example of this optical modulator is a micro-mirror type optical modulator such as the digital micro-mirror device (a trade mark of TI (Texas Instruments, Co.), hereinafter referred to as “DMD”).
The DMD has a plurality of micro-mirrors corresponding to a plurality of pixels forming an image. The inclination of each of the plurality of micro-mirrors varies according to image information. The light is reflected according to the inclination of each micro-mirror. Of the light reflected by each micro-mirror, light reflected in a predetermined direction is utilized as the light for forming an image.
FIGS.
11
(A)-(D) are diagrams illustrating the DMD and prism in a conventional projector. FIGS.
11
(A),
11
(B),
11
(C) and
11
(D) are a front view, a plan view, a right side view, and a perspective view, respectively. A prism
600
is arranged in the proximity of a light illumination surface
502
of a DMD
500
. An axis parallel to a central axis
500
ax perpendicular to the light illumination surface
502
of the DMD
500
is the z-axis, and the direction from the DMD
500
to the prism
600
is the normal direction. Further, of the axes which are perpendicular to the z-axis and orthogonal to each other, the horizontal axis is the x-axis and the vertical axis is the y-axis.
In the following description, to facilitate the illustration, the illumination light incident on the center of the light illumination surface
502
will be described. That is, in the following description, each illumination light indicates the central beam (central axis) of each illumination light. Illumination light I
1
emitted from an illumination optical system (not shown) impinges upon the prism
600
. The illumination light I
1
incident on the prism
600
undergoes total reflection at the selective reflection/transmission surface
620
of the prism
600
. Illumination light I
2
which has undergone total reflection at the selective reflection/transmission surface
620
is applied to the light illumination surface
502
of the DMD
500
. The DMD
500
reflects the illumination light I
2
applied to the light illumination surface
502
according to image information. Of the illumination light reflected by the DMD
500
, illumination light I
3
reflected in the z-direction is utilized as the light representing the image. The to illumination light I
3
emitted from the DMD
500
impinges upon the prism
600
, is transmitted through the selective reflection/transmission surface
620
, and emitted to the projection optical system (not shown). The light impinging upon the projection optical system is projected to display the image.
The inclination of each micro-mirror varies in a see-saw-like manner about an axis parallel to the M-axis of FIG.
11
(A), in response to an electric signal. In order that each pixel may be switched on and off by this inclination of the micro-mirror, there is a predetermined restriction to the incident angle of the illumination light incident on the DMD. That is, as shown in FIG.
11
(A), when the optical path of each illumination light is projected onto the xy-plane parallel to the light illumination surface
502
, the optical path of the illumination light I
2
incident on the light illumination surface
502
is set so as to be directed obliquely downward to the right at an angle of approximately 45 degrees with respect to the central axis Lx parallel to the x-axis. Further, as shown in FIG.
11
(D), in the plane including the illumination light I
2
and the modulated light I
3
, the incident angle of the illumination light I
2
incident on the light illumination surface
502
is set so as to be approximately 20 degrees.
In the prism
600
, to satisfy the above restriction, as shown in FIG.
11
(A), when the optical path of the illumination light I
1
incident on the selective reflection/transmission surface
620
is projected onto the xy-plane, it is set so as to be parallel to the optical path of the illumination light I
2
. Thus, the illumination optical system emitting the illumination light I
1
is usually arranged obliquely downward to the right at an angle approximately 45 degrees. As a result, in the conventional projector using a DMD as the electro-optic device, a space is needed not only in the horizontal direction but only in the vertical direction as the space for arranging the illumination optical system, making it difficult to reduce the thickness of the projector.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a technique for reducing the size of a projector of the type which uses an optical modulator which modulates light by controlling the emitting direction of light applied to the light illumination surface according to the image information, as in the case of a DMD.
To achieve the above object, there is provided, in accordance with the present invention, a projector which may consist of:
an illumination optical system that emits illumination light;
an optical modulator having a light illumination surface that controls an emerging direction of the light applied to the light illumination surface in accordance with image information to modulate the light applied to the illumination surface;
a projection optical system that projects light emitted from the optical modulator; and
a prism provided between the optical modulator and the projection optical system.
The prism has a selective reflection/transmission surface that reflects the illumination light emitted from the illumination optical system to cause the illumination light to impinge upon the light illumination surface at a predetermined angle, and that transmits the light emitted from the optical modulator and that emits the light emitted from the optical modulator to the projection optical system. The selective reflection/transmission surface is formed such that, when the optical paths of the illumination light are projected onto a plane parallel to the light illumination surface, the inclination of the central axis of the illumination light emitted from the illumination optical system and impinging upon the selective reflection/transmission surface is different from the inclination of the central axis of the illumination light reflected by the selective reflection/transmission surface and impinging upon the light illumination surface.
In the projector of the present invention, the illumination optical system can be arranged such that, when the optical path of illumination light is projected onto a plane parallel to the light illumination surface, the inclination of the central axis of the illumination light emitted from the illumination optical system and impinging upon the selective reflection/transmission surface differs from the inclination of the central axis of the illumination light reflected by the selective reflection/transmission surface and impinging upon the light illumination surface, whereby the size of the projector can be reduced.
In the above projector, an arrangement may be adopted wherein the light illumination surface has a substantially rectangular contour. When an optical path of the illumination light is projected onto a plane parallel to the light illumination surface, the central axis of the illumination light reflected by the selective reflection/transmission surface and impinging upon the light illumination surface is inclined approximately 45 degrees with respect to a side of the contou
Kato Hisamaro
Nishida Kazuhiro
Takizawa Takeshi
Ushiyama Tomiyoshi
Kostak Victor R.
Oliff & Berridge PLC.
Seiko Epson Corporation
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