Optics: image projectors – Polarizer or interference filter
Patent
1998-01-27
2000-03-14
Dowling, William
Optics: image projectors
Polarizer or interference filter
353 38, 353 31, G03B 2114
Patent
active
060363185
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a projection type display apparatus for projecting and displaying a display image formed by a reflection type modulation element such as a reflection type liquid crystal device on a projection surface.
DESCRIPTION OF THE RELATED ART
Nowadays, there have been well known projection type display apparatuses using a liquid crystal device as a light valve as a method of displaying a large image. FIG. 14 shows an example of the typical arrangement of a projection type display apparatus using three liquid crystal devices as an example of the projection type display apparatuses. A light source unit 110 is composed of a light source lamp 111 and a paraboloidal reflector 112. The light emitted from the light source lamp 111 is reflected at the paraboloidal reflector 112 and enters a dichroic mirror 401. The light is separated to three color lights, that is, red light, green light and blue light by two dichroic mirrors 401, 402 having a wavelength selection property. These color lights illuminate transmission type liquid crystal devices 301R, 301G, 301B corresponding to the respective color lights. The lights pass through the respective transmission type liquid crystal devices, are combined by a cross-dichroic prism 420, and are projected to and displayed on a projection surface 600 through a projection optical system 500. Note, reflection mirrors 403, 404, 405 for reflecting light beams are disposed in the light path of the red light and the light path of the blue light.
A dichroic film is disposed in an X-shape on the cross-dichroic prism 420 used as color combination means. The color combination means of the projection type display apparatus using the three liquid crystal devices can be also realized by the use of two dichroic mirrors in place of the cross-dichroic prism 420. However, the arrangement using the cross-dichroic prism 420 has a feature that a bright projected image can be obtained even if a large diameter projection lens is not used because the distances between the liquid crystal devices 301R, 301G, 301B and the projection optical system 500 can be shortened as compared with the arrangement where the two dichroic mirrors are disposed in parallel with each other.
In the conventional projection type display apparatuses, however, the length of the light path of the light separating portion is considerably increased because dichroic mirrors 401, 402 and reflection mirrors 403, 404, 405 are used, although the length of the light path of the light combining portion can be shortened by the use of the cross-dichroic prism 420. Therefore, the conventional projection type display apparatus has a large amount of light loss in a light separating process and cannot sufficiently make use of the characteristics of the cross-dichroic prism 420.
Further, since the light beams emerging from the light source unit 110 composed of the light source lamp 111 and the paraboloidal reflector 112 have an uneven light intensity distribution in the cross-sectional area thereof, they have such characteristics that the intensity of the illuminating light is large in the vicinity of the optical axis of the light source and is gradually reduced with distance from the optical axis. Therefore, the conventional projection type display apparatus as shown in FIG. 14 has a problem that the light intensity distribution of the illuminating light is uneven in the liquid crystal devices 301R, 301G, 301B as the regions to be illuminated and the image projected to a projection surface 600 have uneven brightness and uneven color.
An object of the present invention is to provide a projection type display apparatus capable of obtaining a brighter projected image by preventing light loss by shortening the length of a light path without the need for using a large diameter projecting lens.
Another object of the present invention is to provide a projection type display apparatus capable of projecting an image having uniform brightness and good quality by lowering the unevenness of the intensi
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patent: 5098184 (1992-03-01), Van Den Brandt et al.
patent: 5601351 (1997-02-01), Van Den Brandt
patent: 5826959 (1998-10-01), Atsuchi
patent: 5865521 (1999-02-01), Hashizume et al.
patent: 5898521 (1999-04-01), Okada
[Development Design] Optical Device, Liquid Crystal, "Matsushita Industrial Co., Ltd. Develops Liquid Crystal Projector with Doubled Brightness; Polarized light converting optical system formed with a simpler structure for installation," Nikkei Mechanical Jan. 6, 1997, No. 497, pp. 18-19.
Dowling William
Seiko Epson Corporation
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