Color image display apparatus

Optics: image projectors – Composite projected image – Multicolor picture

Reexamination Certificate

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Details

C353S034000, C353S037000, C359S201100, C359S204200, C359S212100, C359S216100, C359S223100

Reexamination Certificate

active

06511184

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a color image display device that displays a color image with one light valve as a light modulating member. Also, the present invention relates to a projection-type image display apparatus including such a color image display device.
BACKGROUND ART
A liquid crystal projector now part of the mainstream in the market of large-screen displays uses a light source lamp, a focusing lens and a projection lens to magnify and form an image of a liquid crystal panel (a light valve) onto a screen. Currently commercialized systems can be classified roughly into a three-plate system and a single-plate system.
In the former system of the three-plate liquid crystal projector, after a light beam from a white light source is separated into light beams of three primary colors of red, green and blue by a color separation optical system, these light beams are modulated by three monochrome liquid crystal panels so as to form images of the three primary colors. Thereafter, these images are combined by a color combination optical system so as to be projected onto a screen by one projection lens. Since the entire spectrum of the white light from the light source can be utilized, this system has a high efficiency of light utilization. However, because of the necessity of the three liquid crystal panels, the color separation optical system, the color combination optical system and a convergence adjusting mechanism between the liquid crystal panels, this system is relatively expensive.
On the other hand, a conventional single-plate system liquid crystal projector is compact and inexpensive because an image formed on a liquid crystal panel having a mosaic color filter simply is magnified and projected onto a screen. However, since this system obtains light with a desired color by absorbing light with an unwanted color out of white light from the light source by using the color filter as a color selection member, only one-third or less of the white light that has entered the liquid crystal panel is transmitted (or reflected). Accordingly, the efficiency of light utilization is low and high-brightness images cannot be obtained easily. When the light source is brightened, the brightness of the displayed image can be improved. However, there remain problems of heat generation and light resistance owing to light absorption by the color filter, making it very difficult to increase the brightness.
In recent years, as a way to eliminate light loss owing to the color filter in this single-plate system, a new configuration in which the efficiency of light utilization is raised by using dichroic mirrors and a microlens array instead of the color filter has been suggested and also commercialized.
A conventional single-plate projection-type image display apparatus, which improves the efficiency of light utilization using the dichroic mirrors and the microlens array, will now be described.
FIG. 30
shows a schematic configuration thereof, and
FIG. 31
shows a detailed cross-section of a light valve of the projection-type image display apparatus shown in FIG.
30
.
A projection-type image display apparatus
900
has a light source portion
901
, an illuminating device
903
, a color separation optical system
907
, a transmission-type light valve
902
and a projection lens
908
. A white light beam from the light source portion
901
irradiates an effective region of the light valve
902
by means of the illuminating device
903
. The color separation optical system
907
includes a red-reflecting dichroic mirror
904
, a green-reflecting dichroic mirror
905
and a total reflection mirror
906
that are arranged obliquely. The white light beam that has passed through the illuminating device
903
enters the color separation optical system
907
, thereby being separated horizontally into three light beams of primary colors of red, green and blue, so as to enter the light valve
902
. The transmission-type light valve
902
has pixels that can modulate the incident light beams of the respective colors independently by an input signal corresponding to each of the red, green and blue light beams, with these pixels being arranged horizontally in one element.
The white light beam emitted from the light source portion
901
is led to the color separation optical system
907
by the illuminating device
903
. A red light beam in the incident light is reflected by the red-reflecting dichroic mirror
904
placed obliquely with respect to the incident light so as to travel along an optical axis
909
. A green light beam in the light transmitted by the red-reflecting dichroic mirror
904
is reflected by the green-reflecting dichroic mirror
905
placed obliquely with respect to the incident light so as to travel along an optical axis
910
. A blue light beam transmitted by the green-reflecting dichroic mirror
905
enters the reflection mirror
906
, and is then reflected so as to travel along an optical axis
911
. The red light beam on the optical axis
909
, the green light beam on the optical axis
910
and the blue light beam on the optical axis
911
pass through a condenser lens
912
and reach the transmission-type light valve
902
.
As shown in
FIG. 31
, an entrance-side polarizing plate
913
is provided as a polarizer on the side of an entrance surface of the transmission-type light valve
902
, and only the light beam having a predetermined polarization direction in the incident light is transmitted by this polarizing plate
913
. The transmitted light enters a microlens array
918
including a group of microlenses
917
with their longitudinal direction being in a vertical direction. The horizontal width of the microlens
917
corresponds to the total horizontal widths of a pixel aperture for red
914
, a pixel aperture for green
915
and a pixel aperture for blue
916
. The red light beam that has traveled along the optical axis
909
and entered the microlens
917
obliquely at an incident angle of &thgr;
1
is focused on the pixel aperture for red
914
. The green light beam that has traveled along the optical axis
910
and whose chief ray entered the microlens
917
at a right angle is focused on the pixel aperture for green
915
. The blue light beam that has traveled along the optical axis
911
and entered the microlens
917
obliquely from the direction opposite to the red light at an incident angle of &thgr;
1
is focused on the pixel aperture for blue
916
. The light beam of each color that has passed through the pixel aperture for each color enters an exit-side polarizing plate
919
provided on an exit surface of the transmission-type light valve
902
. The exit-side polarizing plate
919
has a polarization axis arranged orthogonal to the polarization axis of the entrance-side polarizing plate
913
. Since a light beam that has entered a pixel aperture to be displayed as white is emitted with its polarization direction being rotated by about 90° in a liquid crystal layer, it is transmitted by the exit-side polarizing plate
919
and reaches the projection lens
908
. Since a light beam that has entered a pixel aperture to be displayed as black is emitted without being subjected to the rotation of its polarization direction in the liquid crystal layer, it is absorbed by the exit-side polarizing plate
919
and does not reach the projection lens
908
. The transmission-type light valve
902
rotates the polarization direction of the incident light at every pixel so as to display an image.
In the single-plate projection-type image display apparatus with the new configuration in which the efficiency of light utilization is raised as described above, it is possible to achieve a high efficiency of light utilization close to that in the three-plate system without wasting the light from the light source.
However, in this configuration, a bright lens whose f-number is smaller than 1/(2 sin (&thgr;2+&thgr;3)) is required as the projection lens
908
, where a half-angle of a cone of rays converging from the microlens
917
toward the pixel aperture is e

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