Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2002-07-23
2003-12-30
Dowling, William (Department: 2851)
Optics: image projectors
Polarizer or interference filter
Reexamination Certificate
active
06669344
ABSTRACT:
This application claims the benefit of Japanese Patent application No. 2001-224668 which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a color synthesizing optical apparatus and a projection type display apparatus, and more particularly to a projection type display apparatus for color-synthesizing a plurality of colors and projecting a full-color image on a screen through a projection lens.
2. Related Background Art
An apparatus disclosed in, for instance, Japanese Patent No. 2599309 is known as a projection type display apparatus constructed to color-synthesize a plurality of colors and to project a full-color image on a screen through a projection lens. In this apparatus, a light source beam emitted from a light source is color-separated into a blue (B) light beam, a green (G) light beam and a red (R) light beam assuming three primary colors by a color separating optical system. The thus color-separated light beams enter polarization beam splitters disposed for the respective colors. Then, the respective S-polarized light beams among the incident light beams are reflected by the polarization separation surfaces of the respective polarization beam splitters and travel toward the respective reflection type light valves disposed for the respective color beams. Each reflection type light valve modulates the incident light beam in accordance with an image signal and lets the modulated light beam exit. The light beams having exited the respective reflection type light valves enter again the respective polarization beam splitters. The polarization separating surfaces of the respective polarization beam splitters transmit only the respective modulated light beams, thereby analyzing the respective color light beams. The thus analyzed color light beams enter a color synthesizing optical system constructed of a cross dichroic prism from surfaces different corresponding to the respective colors. Then, the color synthesizing optical system color-synthesizes the analyzed color light beams and lets these light beams exit toward the projection lens. The projection lens projects on the screen a full-color light image of images generated on the reflection type light valves.
Further, U.S. Pat. No. 5,327,270 (Japanese Patent Post-Exam Publication No.7-38050) discloses an architecture for improving a contrast of the projected image on the projection type display apparatus having the construction described above. This architecture is that, for each color, a quarter wave plate is disposed in a light path between the polarization beam splitter serving as a polarizer and an analyzer and the reflection type light valve. Then, the quarter wave plate is disposed so that a phase advance axis (fast axis) or a phase delay axis (slow axis) of the quarter wave plate is orthogonal to a plane containing an incident optical axis and a reflection optical axis of the polarization beam splitter.
The projection type display apparatus in the prior art, however, has a problem in which ununiformity in color occurs at four corners of the projected image projected on the screen. The occurrence of the ununiformity in color is conspicuous especially when the projected color light beam assumes a half tone.
SUMMARY OF THE INVENTION
It is a primary object of the present invention, which was devised to obviate the above problem, to provide a color synthesizing optical apparatus and a projection type display apparatus that are capable of reducing ununiformity in color of a projected image.
To accomplish the above object, according to the first invention, a color synthesizing optical apparatus comprises:
a plurality of reflection type light valves modulating incident light beams on the basis of image signals and letting the modulated beams exit;
a color synthesizing/analyzing optical system including polarization beam splitters corresponding to the plurality of reflection type light valves, and color-synthesizing and analyzing the light beams having exited the plurality of reflection type light valves; and
quarter wave plates disposed corresponding to the plurality of reflection type light valves in light paths extending from exit surfaces of the reflection type light valves to incident surfaces of the polarization beam splitters;
wherein a first light valve group is constructed of the reflection type light valve(s) that lets (let) the beam(s) exit, which makes (make) none of reflection or is (are) reflected an even number of times in the light paths till the light beams exit the color synthesizing/analyzing optical system since the light beam(s) exited the reflection type light valve(s), a second light valve group is constructed of the reflection light valve(s) that lets (let) the beam(s) exit, which is (are) reflected an odd number of times in the light paths till the light beams exit the color synthesizing/analyzing optical system since the light beam(s) exited the reflection type light valve(s);
in a state where the first light valve group and the second light valve group are being energized to effect image-displaying, in one group of the first light valve group and the second light valve group, phase advance axis (axes) of the quarter wave plate(s) is (are) disposed substantially in parallel to predetermined axis (axes) within surface(s) of the reflection type light valve(s) which axis (axes) correspond to the predetermined axis (axes) within the projection image field planes of said light valve(s); and
in the other group of the first light valve group and the second light valve group in the same state, phase advance axis (axes) of the quarter wave plates is (are) disposed substantially perpendicularly to the predetermined axis (axes) within the surface(s) of the reflection type light valve(s) which axis (axes) correspond to the predetermined axis (axes) within the projection image field plane(s) of said light valve(s).
In the color synthesizing optical apparatus according to the first invention, the beams of light polarization-separated and color-separated in a polarization separating/color separating optical system enter the plurality of reflection type light valves.
According to the second invention, a projection type display apparatus comprises:
a light source supplying light beams;
a polarization separating/color separating optical system effecting polarization separation and color separation with respect to a light beam emitted from the light source;
a plurality of reflection type light valves modulating incident light beams on the basis of image signals and letting the modulated light beams exit;
a color synthesizing/analyzing optical system including polarization beam splitters corresponding to the plurality of reflection type light valves, and color-synthesizing and analyzing the light beams having exited the plurality of reflection type light valves;
quarter wave plates disposed corresponding to the plurality of reflection type light valves in light paths extending from exit surfaces of the reflection type light valves to incident surfaces of the polarization beam splitters; and
a projection optical system projecting images generated on the plurality of reflection type light valves,
wherein a first light valve group is constructed of the reflection type light valve(s) that lets (let) the light beam(s) exit, which makes (make) none of reflection or is (are) reflected an even number of times in the light paths till the light beams exit the color synthesizing/analyzing optical system since the light beam(s) exited the reflection type light valve(s);
a second light valve group is constructed of the reflection light valve(s) that lets (let) the light beam(s) exit, which is (are) reflected an odd number of times in the light paths till the light beams exit the color synthesizing/analyzing optical system since the light beams exited the reflection type light valves;
in a state where the first light valve group and the second light valve group are being energized to effect image-displaying,
with respect to one of said first light va
Dowling William
Miles & Stockbridge P.C.
Nikon Corporation
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