Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
1999-10-06
2001-12-18
Dowling, William (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S020000, C349S005000
Reexamination Certificate
active
06331060
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection-type display device which can be applied to for example a projector device for projecting an optical image spatially modulated by reflection-type liquid crystal panels onto a screen.
2. Description of the Related Art
In the related art, a projection-type display device has been proposed which is configured to use reflection-type liquid crystal panels to generate spatially modulated optical images and to project the optical images onto a screen so as to form a desired color image.
Among such projection-type display devices, ones have been proposed which use dichroic mirrors or use dichroic prisms as the means for breaking down illumination light obtained from a light source into red, blue, and green illumination light for supply to corresponding reflection-type liquid crystal panels and for synthesizing the red, green, and blue optical images obtained from the reflection-type liquid crystal panels.
FIG. 1
is a view of the configuration of a projection-type display device using dichroic prisms.
In this projection-type display device
1
using dichroic prisms, as shown in
FIG. 1
, a light source
2
is comprised for example a discharge lamp
3
and a reflector
4
and emits white illumination light.
Further, the light source
2
uses fly eye lenses
5
A and
5
B to make the distribution of the amount of the illumination light uniform, then emits the light to a plane polarization conversion element
6
. Here, the plane polarization conversion element
6
selectively transmits mainly the s-polarization component and converts the p-polarization component orthogonal to this to the s-polarization component.
Due to this, the light source
2
emits illumination light increased in the polarization component effective for the image display in the illumination light projected from the discharge lamp
3
by the various plane polarizations and reduced in the polarization component orthogonal to this. As a result, the efficiency of utilization of the illumination light is improved by that extent and the contrast of the display image is improved.
A convex lens
7
converges and emits this illumination light on the path of the illumination light emitted from the plane polarization conversion element
6
.
A cold mirror
8
emits the components of the illumination light emitted from the convex lens
7
other than the infrared region reflected in a direction 90 degrees from the path of incidence.
A convex lens
9
converges and emits the illumination light reflected at the cold mirror
8
.
A polarization beam splitter
11
is formed by adhering inclined planes of rectangular prisms to each other and is formed with a detecting plane
11
A at the adhered planes. The polarization beam splitter
11
selectively reflects and emits from the detecting plane
11
A the illumination light due to the s-polarized light emitted from the convex lens
28
, while selectively transmits the p-polarization component in the synthesized optical image incident on it traveling back along the path of the illumination light due to the s-polarized light and returns the s-polarization component to the light source
2
.
A dichroic prism
12
is formed by adhering inclined planes of three prisms each having a predetermined form to each other and is arranged so that the adhered planes out across the path of the light projected from the polarization beam splitter
11
. The dichroic prism
12
is formed with dichroic films MB, MR obtained by lamination of dielectric films to a predetermined thickness on the adhered planes cutting across the optical path. The blue and red illumination light in the illumination light projected from the polarization beam splitter
11
are successively selectively reflected at the dichroic films MB, MR. Due to this, the dichroic prism
12
breaks down the illumination light projected from the polarization beam splitter
11
into blue, red, and green illumination light and supplies them to the blue, red, and green color reflection-type liquid crystal panels
13
B,
13
R, and
13
G arranged at the bottom surface of the prism.
The reflection-type liquid crystal panels
13
B,
13
R, and
13
G are driven by corresponding color signals. The illumination light incident by the s-polarized light is reflected with the plane polarization rotated for every pixel. Due to this, optical images changed in plane polarization in accordance with the color signals are projected.
The dichroic prism
12
, conversely to the case of the illumination light, synthesizes the blue, red, and green optical images obtained from the reflection-type liquid crystal panels to generate a synthesized optical image and projects the synthesized optical image to the polarization beam splitter
11
.
Specifically, the synthesized optical image travels back along the path of the illumination light due to the synthesized light of the p-polarized light and s-polarized light in accordance with the color signals and is emitted to the polarization beam splitter
11
. Further, only the p-polarization component in the synthesized optical image passes through the polarization beam splitter
11
and is projected to the projection lens
14
.
In this way, the projection lens
14
projects the synthesized optical image passing through the polarization beam splitter
11
to the screen
15
. Due to this, a color image is displayed by enlarging and projecting onto the screen the images generated by the reflection-type liquid crystal panels
13
B,
13
R, and
13
G.
Further, a projection-type display device using diehroic mirrors is configured to break down the illumination light incident from a polarization beam splitter into red, blue, and green illumination light by dichroic mirrors instead of the dichroic prisms
12
and project them onto the reflection-type liquid crystal panels and to synthesize the optical images projected from the reflection-type liquid crystal panels and emit the result on a projection lens.
In this type of projection-type display device
1
, however, there has been the disadvantage that the so-called haze phenomenon occurs where light is also projected at portions which should inherently be displayed black and those portions are displayed whitish and this haze phenomenon causes a reduction in the contrast of the projected image.
The haze phenomenon will be explained in further detail below.
In the projection-type display device
1
, the portion which inherently should be displayed black is reflected without any rotation of the plane polarization of the corresponding illumination light at the reflection-type liquid crystal panels. As a result, in the projection-type display device
1
, the corresponding optical images are returned to the light source
2
side by the polarization beam splitter
11
. Due to this, the corresponding portion should be displayed black on the screen
15
.
In the projection-type display device
1
, however, this type of optical image which should be detected at the polarization beam splitter
11
by the s-polarized light is detected by the synthesized light of the s-polarized light and the p-polarized light. Due to this, this type of haze phenomenon is generated.
That is, in an optical system provided with a polarization beam splitter
11
, dichroic prisms
12
, etc., a phase difference is given in the direction of vibration of the light to the p-polarized light parallel to the boundary planes and the s-polarized light orthogonal to the p-polarization component using as a reference the incidence plane and emission plane of the polarization beam splitter
11
, the light detecting plane, the boundary plane of the dichroic film etc. Due to this, in this type of projection-type display device, when viewed as an optical system as a whole, the direction of the p-polarization component initially separated by the polarization beam splitter
11
changes at the boundary planes. Further, the phase difference generated at the boundary planes in this way changes by the incident wavelength and angle of incidence to the
Miyawaki Tetsuyuki
Yamamoto Hideki
Bell Boyd & Lloyd LLC
Dowling William
Sony Corporation
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