Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
1999-03-23
2001-01-23
Dowling, William (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S020000, C349S009000
Reexamination Certificate
active
06176586
ABSTRACT:
This application is based on applications Nos. H10-076104 and H10-077377 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection display apparatus employing eflection-type liquid crystal display devices.
2. Description of the Prior Art
Conventionally, various display apparatuses of the so-called projection type have been proposed. For example, Japanese Laid-Open Patent Application H2-74903 proposes an arrangement that employs an optical system in which illumination light is separated into beams of different colors and these beams are integrated together by a color integration system including a polarizing beam splitter, a liquid crystal display device, and a cross-dichroic prism. Japanese Laid-Open Patent Application H8-122772 describes, as prior art, an arrangement that employs an optical system composed of three reflection-type liquid crystal display devices, a polarizing beam splitter, and two dichroic mirrors. This Japanese Laid-Open Patent Application H8-122772 proposes an arrangement that employs an optical system composed of three reflection-type liquid crystal display devices and a polarizing beam splitter.
However, the above-mentioned optical system including a cross-dicliroic prism is unduly expensive, because the cross-dichroic prism itself is expensive. The above-mentioned optical system having three reflection-type liquid crystal display devices, a polarizing beam splitter, and two dichroic mirrors requires that the two dichroic mirrors be disposed between the polarizing beam splitter and the reflection-type liquid crystal display devices. This makes the back focal length, i.e. the distance from the projection lens to the reflection-type liquid crystal display devices, unduly long, and thus makes the f-number of the projection lens unduly large, making it impossible to obtain satisfactory brightness.
The above-mentioned optical system proposed in Japanese Laid-Open Patent Application H8-122772 lets unpolarized light enter the polarizing beam splitter, and therefore suffers from flare caused in the projected image by unused polarized-light components. Moreover, this optical system discards the P-polarized light component included in the green component and the S-polarized light component included in the red and blue components without using them for image formation, and thus suffers from inefficient use of the light source.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an inexpensive, compact, and efficient projection display apparatus having a simple structure and offering high contrast and high quality in the projected image.
To achieve the above object, according to one aspect of the present invention, a projection display apparatus is provided with: a first dichroic reflecting surface for separating a polarized light beam into a light beam of a first wavelength range and a light beam of a second wavelength range; a wavelength plate for rotating a polarization plane of the light beam of the first wavelength range; a second dichroic reflecting surface for integrating together the light beam of the first wavelength range after rotation of its polarization plane and the light beam of the second wavelength range; a first polarizing beam splitter for reflecting one and transmitting the other of the light beams of the first and second wavelength ranges after integration by the second dichroic reflecting surface; a first reflection-type liquid crystal display device for modulating and reflecting a light beam reflected from the first polarizing beam splitter; and a second reflection-type liquid crystal display device for modulating and reflecting a light beam transmitted through the first polarizing beam splitter. Here, the first polarizing beam splitter transmits a light beam coming from the first reflection-type liquid crystal display device and reflects a light beam coming from the second reflection-type liquid crystal display device so as to integrate together those two light beams.
According to another aspect of the present invention, an illumination optical system is provided with: separating means for separating a light beam from a light source into a light beam of a first wavelength range and a light beam of a second wavelength range; processing means for optically processing the light beam of the first or second wavelength range; and separating/integrating means for separating a light beam of a third wavelength range from the light beam of the second wavelength range and integrating together a portion of the light beam of the second wavelength range that remains after separation of the light beam of the third wavelength range and the light beam of the first wavelength range.
According to still another aspect of the present invention, a projection display apparatus is provided with: a first dichroic reflecting surface for separating a source light beam into a light beam of a first wavelength range and a light beam of a second wavelength range; a dichroic polarizing beam splitter that transmits the light beams of the first and second wavelength ranges shone onto it from different directions from each other; a first reflection-type liquid crystal display device for modulating and reflecting one of the light beams of the first and second wavelength ranges transmitted through the dichroic polarizing beam splitter; and a second reflection-type liquid crystal display device for modulating and reflecting the other of the light beams of the first and second wavelength ranges transmitted through the dichroic polarizing beam splitter. Here, the dichroic polarizing beam splitter transmits a light beam coming from the first reflection-type liquid crystal display device and reflects a light beam coming from the second reflection-type liquid crystal display device so as to integrate together those two light beams.
Alternatively, a projection display apparatus is provided with: a first dichroic reflecting surface for separating a source light beam into a light beam of a first wavelength range and a light beam of a second wavelength range; a dichroic polarizing beam splitter that reflects the light beams of the first and second wavelength ranges shone onto it from different directions from each other; a first reflection-type liquid crystal display device for modulating and reflecting one of the light beams of the first and second wavelength ranges reflected from the dichroic polarizing beam splitter; and a second reflection-type liquid crystal display device for modulating and reflecting the other of the light beams of the first and second wavelength ranges reflected from the dichroic polarizing beam splitter. Here, the dichroic polarizing beam splitter reflects a light beam coming from the first reflection-type liquid crystal display device and transmits a light beam coming from the second reflection-type liquid crystal display device so as to integrate together those two light beams.
REFERENCES:
patent: 5365287 (1994-11-01), Vollmer et al.
patent: 5374968 (1994-12-01), Haven et al.
patent: 5577826 (1996-11-01), Kasama et al.
patent: 5798819 (1998-08-01), Hattori et al.
patent: 5826959 (1998-10-01), Atsuchi
patent: 6028703 (2000-02-01), Sekine et al.
patent: 6034818 (2000-03-01), Sedmayr
patent: 2-074903 (1990-03-01), None
patent: 8-122772 (1996-05-01), None
patent: 10-010467 (1998-01-01), None
Hayashi Kohtaro
Hirose Naoki
Dowling William
Minolta Co. , Ltd.
Sidley & Austin
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