Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
1999-08-12
2002-01-29
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S008000, C353S009000, C353S031000, C353S094000, C355S032000, C355S067000, C355S071000
Reexamination Certificate
active
06341867
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polarized light illumination apparatus for uniformly illuminating a rectangular illumination area with light polarized in the same direction, and also to a projector using such a polarized light illumination apparatus. More particularly, the present invention relates to a structure for combining lights emitted from two light sources such that the resultant combined light is polarized in the same direction.
2. Description of Related Art
In liquid crystal display devices using a modulating element such as a liquid crystal element which modulates light polarized in a particular direction, only one component of two types of polarized light components included in light emitted from a light source is used. To obtain a projected image with high brightness, it is required to increase the utilization efficiency of light. However, when a projector is constructed using a single light source, the utilization efficiency of light has a practical upper limit. Thus, one technique of projecting a high-brightness image is to increase the amount of light by using a plurality of light sources.
However, if a plurality of light sources are arranged in a simple fashion, the overall area of the light source image becomes greater by a factor corresponding to the number of light sources. As a result, the angle of light (illumination angle) striking an illumination area also increases by a corresponding factor. This means that the amount of light per unit area is the same as that obtained with a single light source. In other words, the amount of light per unit area cannot be increased by using a plurality of light sources arranged in the above-described fashion.
Even when the amount of light can be increased by using a plurality of light sources, if only one component of two polarized light components of light emitted from the light sources is used, one-half of the total amount of light is wasted, which reduces its effectiveness by half.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a polarized light illumination apparatus including a plurality of light sources and capable of emitting light using both polarized light components without causing an increase in the illumination angle. It is another object of the present invention to provide a projector capable of forming a projected image with extremely high brightness.
To solve the issues described above, the present invention provides a polarized light illumination apparatus comprising:
first and second light sources;
a polarized light separating and combining optical element including: a first polarization separating film which transmits a linearly polarized light contained in light emitted from the first light source and polarized in a direction parallel to an incidence plane but which reflects a linearly polarized light contained in the light emitted from the first light source and polarized in a direction perpendicular to the incidence plane; and a second polarization light separating film which transmits a linearly polarized light contained in light emitted from the second light source and polarized in a direction parallel to the incidence plane but which reflects a linearly polarized light contained in light emitted from the second light source polarized in a direction perpendicular to the incidence plane;
a first condensing and reflecting optical element including a plurality of small condensing and reflecting elements for substantially reversing the traveling direction of the linearly polarized light transmitted through the first polarization separating film and forming a condensed light image;
a second condensing and reflecting optical element including a plurality of small condensing and reflecting elements for substantially reversing the traveling direction of the light reflected by the first polarization separating film and the second polarization separating film and forming a condensed light image;
a third condensing and reflecting optical element including a plurality of small condensing and reflecting elements for substantially reversing the traveling direction of the linearly polarized light transmitted through the second polarization separating film and forming a condensed light image;
a first polarization-state conversion optical element disposed between the polarized light separating and combining optical element and the first condensing and reflecting optical element;
a second polarization-state conversion optical element disposed between the polarized light separating and combining optical element and the second condensing and reflecting optical element;
a third polarization-state conversion optical element disposed between the polarized light separating and combining optical element and the third condensing and reflecting optical element; and
a polarization conversion optical element for aligning the direction of polarization of the linearly polarized lights combined by the polarized light separating and combining optical element; the polarized light illumination apparatus being characterized in that a center axis of the light which is incident on the polarization conversion optical element after being reflected by the small condensing and reflecting elements of the first and third condensing and reflecting optical elements and a center axis of the light which is incident on the polarization conversion optical element after being reflected by the small condensing and reflecting elements of the second condensing and reflecting optical element are parallel to each other and do not overlap each other.
The construction of the polarized light illumination apparatus according to the present invention is described in further detail below.
Of the components of the light polarized in random directions (hereinafter, referred to as the randomly polarized light) emitted from the first light source, a linearly polarized light component polarized in a direction parallel to the incidence plane passes through the first polarization separating film, whereas a linearly polarized light component polarized in a direction perpendicular to the incidence plane is reflected by the first polarization separating film. On the other hand, of the components of the randomly polarized light emitted from the second light source, a linearly polarized light component polarized in a direction parallel to the incidence plane passes through the second polarization separating film, whereas a linearly polarized light component polarized in a direction perpendicular to the incidence plane is reflected by the second polarization separating film. Herein, the “incidence plane” is a technical term used in the art of optics to represent a virtual plane including the center axis of a light incident on a film, and also including the normal to the film.
The linearly polarized light which has passed through the first polarization separating film passes through the first polarization-state conversion optical element and is then reflected by the first condensing and reflecting optical element back to the first polarization-state conversion optical element. The light again passes through the first polarization-state conversion optical element and travels toward the polarized light separating and combining optical element. In the above process, the light is divided by the first condensing and reflecting optical element into a plurality of intermediate lights and converted to linearly polarized lights with a polarization rotated by about 90° when the light passes twice through the first polarization-state conversion optical element. Thus, when the light returns to the polarized light separating and combining optical element, the light is reflected by the first polarization separating film and directed toward the polarization conversion optical element. Herein, the polarized light directed toward the polarization conversion optical element is referred to as first polarized light.
The linearly polarized light reflected by the first polarization separating film and the
Brown Khaled
Oliff & Berridg,e PLC
Seiko Epson Corporation
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