Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2002-07-17
2004-05-04
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S031000, C353S102000, C349S009000
Reexamination Certificate
active
06729730
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a projector which divides light from a light source into a plurality of partial light beams, which converts the plurality of partial light beams into one type of polarized light beam polarized in substantially the same direction by a polarization conversion element, which changes the polarized state of the polarized light beam by an electro-optical device, which selects a state by a polarization selection element to form an optical image according to image information, and which enlarges and projects the optical image.
2. Description of Related Art
Recently, attention has been focused on projectors using a reflective-type liquid crystal device. In such a reflective-type liquid crystal device, the pixel density can be increased by forming a structure, such as a transistor, for driving liquid crystal under a reflecting mirror. Therefore, the reflective-type liquid crystal device has the advantage of realizing a clear projected image with high resolution, compared with the case where a transmissive liquid crystal device is used.
In addition, in projectors using an electro-optical device, such as a liquid crystal device, in order to reduce the size of the entire device while realizing a bright projected image without display nonuniformity, the use of an integrator optical system or a polarization conversion element has been proposed (Japanese Unexamined Patent Application Publication No. 8-34127, and Japanese Unexamined Patent Application Publication No. 10-232430, etc.). In the integrator optical system, light from a light source is divided by a light beam dividing optical element into a plurality of partial light beams to form a plurality of light source images, the light source images are considered as dummy light sources, and light from the plurality of light source images is superposed on a liquid crystal panel, whereby illumination light having a uniform intensity distribution can be obtained. In the polarization conversion element, light from a light source is divided into a plurality of partial light beams to perform polarization conversion and then, the light is superimposed on a liquid crystal device, whereby illumination light polarized in the same direction is obtained.
For this reason, it is thought that a brighter projected image with high resolution and without display nonuniformity can be realized if the integrator optical system and the polarization conversion element are used in combination in the projector using the reflective-type liquid crystal device.
SUMMARY OF THE INVENTION
When a reflective-type liquid crystal device utilizing a polarization mode as a display mode is used in a projector, a polarization selection element (for example, a polarization beam splitter) for spatially separating and selecting light of different polarization states is generally used, but the polarization selecting characteristic of the polarization selection element has strong incident-angle-dependency. More specifically, in the case where a plane of incidence including a nearly central axis of the incident light and a normal line of a polarization selection surface of the polarization selection element is defined, if the incident angle of light is increased in a plane perpendicularly intersecting the plane of incidence, the polarization selectivity is substantially reduced. Since this phenomenon greatly depends on a geometrical positional relationship between a polarization selection surface and the light entering there, it is very difficult to prevent the substantial reduction in the polarization selectivity. On the other hand, if the incident angle of light is increased at the plane of incidence, the polarization selectivity is also reduced, but the degree of reduction is relatively small as compared to that in the plane perpendicularly intersecting the plane of incidence, and the reduction in the polarization selectivity can be prevented by arranging the configuration of the polarization selection surface. Therefore, in order to at least improve the polarization selectivity of the polarization selection element, it is important to reduce the incident angle of light in the plane perpendicularly intersecting the plane of incidence as much as possible, for example.
In addition, the optical system employing the integrator optical system or the polarization conversion element, by reason of its optical process, cannot avoid the phenomenon in which the angular distribution of the incident angle of illumination light expands.
For this reason, in the case where the integrator optical system and the polarization conversion element are used in combination in the projector using the reflective-type liquid crystal device, since the incident angle of light entering the polarization selection surface is increased, the polarization selectivity of the polarization selection surface is reduced, causing a problem in that light utilization efficiency is reduced and non-uniform brightness occurs.
It is one object of the present invention to at least provide a projector which can realize a bright projected image with high light utilization efficiency and high quality while combining a reflective-type liquid crystal device and an integrator optical system or a polarization conversion element.
The projector according to the present invention achieves at least the above object by, for example, arranging a direction of polarization beam separation and characteristics of a light beam dividing optical element.
(1) The projector according to one exemplary embodiment of the present invention is a projector including a light beam dividing optical element for dividing light from a light source into a plurality of partial light beams; a polarization conversion element for converting the plurality of partial light beams into one type of polarized light beam polarized substantially in the same directions; an electro-optical device for modulating an illumination light beam emitted from the polarization conversion element; a projection lens for projecting light modulated by the electro-optical device; and a polarization selection surface for selecting light of a predetermined polarized component included in the illumination light beam and emitting the light toward the electro-optical device, and for selecting light of a predetermined polarized component in the light modulated by the electro-optical device and emitting the light toward the projection lens. In the projector, when a plane of incidence including a normal line of the polarization selection surface and the central axis of the illumination light beam is assumed, the direction parallel to the plane of incidence and perpendicularly intersecting the central axis is defined as the X-axis direction, and the direction perpendicularly intersecting the plane of incidence is defined as the Y-axis direction, the direction of polarization beam separation by the polarization conversion element is the X-axis direction.
According to the exemplary embodiment as described above, the polarization beam separability of the polarization selection surface has strong incident-angle-dependency to an incident light beam. In particular, when an incident angle of light is increased in the Y-axis direction perpendicularly intersecting the plane of incidence, the polarization selectivity is remarkably reduced. On the other hand, in the polarization conversion element, since two types of polarized light beams polarized in different directions are produced from the partial light beams, the width of each partial light beam substantially doubles in the direction of separation, and the angular distribution of the light expands. Thus, in order to improve the polarization selectivity in the polarization selection element, it is important to consider the incident-angle-dependency of the polarization selectivity and the spread of the angular distribution of the light incident thereon.
According to this exemplary embodiment, since the direction of polarization beam separation in the polarization conversion el
Adams Russell
Koval Melissa J
Oliff & Berridg,e PLC
Seiko Epson Corporation
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