Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2000-01-20
2002-12-24
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S031000, C353S037000, C353S038000, C349S005000, C349S009000
Reexamination Certificate
active
06497485
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projector for projecting and displaying a display image formed by a reflection-type modulation device, such as a reflection-type liquid crystal device, on a projection plane.
2. Description of Related Art
Nowadays, a projector using a transmissive liquid crystal device as a light valve is well known as a method for displaying a large screen image. As an example of such a projector, a typical construction of a projector using three transmissive liquid crystal devices is shown in FIG.
12
.
A light source
110
is composed of a light source lamp
111
and a paraboloidal reflector
112
, and light emitted from the light source lamp
111
is reflected by the paraboloidal reflector
112
to enter a dichroic mirror
401
. The light is separated into red light, green light, and blue light by two dichroic mirrors
401
and
402
, each having wavelength-selectivity, and then illuminates transmissive liquid crystal devices
301
R,
301
G, and
301
B corresponding to each color light. The light transmitted by each of the transmissive liquid crystal devices is synthesized by a cross-dichroic prism
420
, and is projected and displayed on a projection plane
600
via a projection optical system
500
. Reflecting mirrors
403
,
404
, and
405
for reflecting light beams are provided on an optical path of the red light and an optical path of the blue light.
In the cross-dichroic prism
420
used as a color-light-synthesizing unit, dichroic films are arranged in the form of an X. The color-light-synthesizing unit of the projector using three liquid crystal devices can be realized by arranging two cross-dichroic mirrors in parallel with each other instead of the cross-dichroic prism
420
. The use of the cross-dichroic prism
420
, however, is characterized by providing a bright projected image without using a large-aperture projection lens because the distance between the liquid crystal devices
301
R,
301
G, and
301
B and the projection optical system
500
can be shortened as compared with a case where the two dichroic mirrors are arranged in parallel with each other.
In the conventional projector, however, while the optical path can be shortened by the use of the cross-dichroic prism
420
in a color-light-synchronization portion, the length of the optical path is considerably long in a color-light-separation portion because the dichroic mirrors
401
and
402
, and the reflecting mirrors
403
,
404
, and
405
are used. Therefore, in the conventional projector, the light loss in a light separating process is large, and characteristics of the cross-dichroic prism
420
cannot be sufficiently utilized.
A light beam emitted from the light source
110
composed of the light source lamp
111
and the paraboloidal reflector
112
has a non-uniform light intensity distribution in a cross section of the light beam, and has characteristics such that the light intensity of illumination light near an optical axis of the light source is high, and the light intensity of the illumination light decreases with distance from the optical axis. Therefore, in the conventional projector shown in
FIG. 12
, the light intensity of the illumination light is non-uniformly distributed on the liquid crystal devices
301
R,
301
G, and
301
B, which are areas to be illuminated, and non-uniform brightness or color shading occurs in an image projected on the projection plane
600
.
Furthermore, when the brightness of the projected image is to be considerably increased using a light source lamp having extremely high optical output, light absorption is large in the liquid crystal devices of the conventional projector using the transmissive liquid crystal devices, and a large-scale cooling device for cooling the liquid crystal devices is absolutely required.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a projector capable of obtaining a bright projected image without using a large-aperture projection lens by shortening the length of an optical path to prevent the loss of light.
In addition, it is an object to provide a projector which reduces non-uniformity of light intensity distribution of illumination light in an area to be illuminated, and which provides uniform brightness and excellent image quality.
Furthermore, it is an object to provide a projector which does not require a large-scale cooling device even if a light source lamp having extremely high optical output is used.
A first projector of the present invention may consist of a light source, a first optical element for condensing a light beam from the light source and dividing the light beam into a plurality of intermediate light beams, a second optical element placed on the light-emitting side of the first optical element for converting the plurality of intermediate light beams into one type of polarized light beams and superimposing the polarized light beams on a reflection-type modulation device, only one reflection-type modulation device for modulating light emitted from the second optical element, a polarized light beam selection element placed on an optical path between the second optical element and the reflection-type modulation device for reflecting or transmitting the light emitted from the second optical element to allow the light to reach the reflection-type modulation device and for transmitting or reflecting the light modulated by the reflection-type modulation device to allow the light to reach a projection optical system, and a collimating lens placed between the second optical element and the polarized light beam selection element.
According to the above construction of the first projector of the present invention, the length of the optical path can be extremely shortened, and the loss of light can be minimized. Therefore, it is possible to obtain an extremely bright projected image without using a large-aperture projection lens.
As the first optical element, a lens array having, for example, a plurality of light beam-dividing lenses arranged in a matrix may be used. By dividing the light beam from the light source into a plurality of intermediate light beams with such a lens array, and by superimposing the intermediate light beams on an area to be illuminated, non-uniform luminance can be further reduced than that of a single light beam. Therefore, even if the light beam emitted from the light source has a non-uniform light intensity distribution within a cross section of the light beam, illumination light having uniform brightness can be obtained. In particular, when the light intensity distribution of the light beam is not random, but the light intensity distribution has a fixed tendency as seen in a light beam emitted from a light source composed of a light source lamp and a paraboloidal reflector, the use of the above first optical element can make the light intensity distribution and angular distribution of the illumination light on the area to be illuminated extremely uniform.
The second optical element separates each of the intermediate light beams into a p-polarized light beam and an s-polarized light beam, aligns the polarization direction, and finally superimposes the light beams on a single area to be illuminated. In the conventional projector, only one of the p-polarized light beam and the s-polarized light beam can be used and the light loss is large in some polarized light beams. If the second optical element of the present invention is used, however, both of the polarized light beams can be used most efficiently. Therefore, it is possible to obtain a bright image. Since the plurality of divided intermediate light beams are finally superimposed on the single area to be illuminated, the polarized light beams having uniform brightness can be obtained as illumination light even if the light beam emitted from the light source has a non-uniform light intensity distribution within the cross section of the light beam. In particular, even if the intermediate light beams cannot be separated into the p-polarized li
Adams Russell
Koval Melissa
Seiko Epson Corporation
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