Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2000-07-06
2002-11-19
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S008000, C353S031000, C353S034000, C353S039000, C349S008000, C349S009000, C349S091000, C349S106000, C349S122000, C359S246000, C359S489040, C359S506000
Reexamination Certificate
active
06481850
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a projector for projecting and displaying an image.
2. Description of Related Art
In a projector, light emitted from an illuminating system is modulated by liquid crystal panels or the like according to image information (image signals), and the modulated light is projected onto a screen, thereby achieving image display.
FIG. 9
is an explanatory view showing a principal part of a conventional projector. The projector may consist of three liquid crystal light valves
900
R,
900
G, and
900
B, a cross-dichroic prism
920
, and a projection system
940
. Light of the three colors red (R), green (G), and blue (B) emitted from an illuminating system (not shown) passes through the liquid crystal light valves
900
R,
900
G, and
900
B, whereby the light is modulated according to image information. The modulated light (modulated light beams) is synthesized by the cross-dichroic prism
920
, and the synthesized light is projected by the projection system
940
. This allows a color image to be displayed on a screen SC.
The first liquid crystal light valve
900
R may include a liquid crystal panel
901
R, and two polarizers
902
Ri and
902
Ro bonded on the side of the light incident surface and on the side of the light emitting surface of the liquid crystal panel
901
R, respectively. The first polarizer
902
Ri on the side of the light incident surface transmits light polarized in the same direction as the polarization axis in the light incident thereon. In
FIG. 9
, since it is assumed that the light incident on the first polarizer
902
Ri is polarized in substantially the same direction as the polarization axis of the first polarizer
902
Ri, almost all of the incident light passes unchanged through the first polarizer
902
Ri. The light transmitted by the first polarizer
902
Ri is converted into light polarized in a predetermined direction by the liquid crystal panel
901
R and the second polarizer
902
Ro, and is emitted. This also applies to the second and the third liquid crystal light valves
900
G and
900
B.
SUMMARY OF THE INVENTION
Incidentally, when light emitted from the illuminating system is applied to the liquid crystal light valves, the polarizers of the liquid crystal light valves usually produce heat. In this case, the temperature of the polarizers is sometimes increased to a high temperature of about 80° C. This is because the light that is not transmitted by the polarizers is absorbed by the polarizers. In
FIG. 9
, since it is assumed that light polarized in substantially the same direction as the polarization axes of the polarizers on the side of the light incident surfaces enters the liquid crystal light valves
900
R,
900
G, and
900
B, the polarizers
902
Ri,
902
Gi, and
902
Bi on the side of the light incident surfaces produce relatively little heat. On the other hand, since the polarizers
902
Ro,
902
Go, and
902
Bo on the side of the light emitting surfaces transmit only the light polarized in a predetermined direction in the light modulated by the liquid crystal panels, and absorb light polarized in other directions, they produce a relatively large amount of heat. If a black image is displayed on the screen SC, the polarizers
902
Ro,
902
Go, and
902
Bo on the side of the light emitting surfaces absorb almost all of the incident light. Therefore, they produce a considerable amount of heat.
When the polarizers produce heat in this way, thermal stress is generated inside the polarizers because the polarizers are bonded to the liquid crystal panels. When the polarizers are bonded to lenses or prisms, thermal stress is similarly generated inside the polarizers.
FIG. 10
is a plan view of the second polarizer
902
Ro bonded on the side of the light emitting surface of the first liquid crystal panels
901
R as viewed from the -x direction. The thermal stress inside the polarizer is exerted in the directions shown by the arrows in
FIG. 10
, and a strain due to the thermal stress is generated in the polarizer. The strain also depends on an intensity distribution of light incident on the polarizer, but usually gets larger, particularly in areas encircled by broken lines shown in
FIG. 10
, that is, at four comers of the nearly rectangular polarizer
902
Ro. When the polarizer strains in this way, the polarizer cannot exhibit desired characteristics. That is, the polarizer
902
Ro may transmit light that should be shielded, or shield light that should be transmitted. In this case, light emitted from a strained portion of the polarizer is elliptically polarized, and the intensity of light may increase or decrease as compared with a normal case in which a linear polarized light is emitted. It is believed that such a phenomenon occurs because of strain generated in the molecular structure of the polarizer, and that such a phenomenon depends on the alignment of liquid crystal molecules that determines the polarization direction of light incident on the polarizer
902
Ro. When the thermal stress is generated in the polarizer
902
Ro in this way, the modulated light beams to be emitted have inconsistencies in brightness. Therefore, when the modulated light beams are synthesized to display a color image on the screen SC, there is a problem in that inconsistencies in color arise in the image. Similarly, when a monochrome image is displayed on the screen SC, there is a problem in that inconsistencies in brightness arise.
This invention is achieved to at least solve the above-described problems in the conventional art. One exemplary object thereof is to provide a technique that is able to at least reduce inconsistencies in an image to be displayed in a projector.
A device in accordance with an exemplary embodiment of the present invention is a projector which may include an illuminating system for emitting illumination light; an electro-optical device for modulating light from the illuminating system according to image information; and a projection system for projecting a modulated light beam obtained by the electro-optical device. In addition, the electro-optical device of this exemplary embodiment preferably includes a polarizer on at least one of the sides of a light incident surface and a light emitting surface, and the polarizer is preferably bonded on a sapphire glass plate.
Since the sapphire glass has high heat conductivity, the temperature rise due to heat produced by the polarizer can be controlled, and the flexion of the polarizer due to thermal stress can be reduced. Therefore, inconsistencies in light emitted from the polarizer can be reduced, and consequently, it is possible to reduce inconsistencies in an image to be displayed.
The sapphire glass plate of this exemplary embodiment may preferably be formed of single-crystal sapphire. Since the single-crystal sapphire glass has particularly high heat conductivity, the above-described advantage is remarkably offered.
In addition, the sapphire glass plate of this exemplary embodiment may preferably be held by a plate member holding portion made of metal. This allows heat produced in the polarizer to be easily radiated to the outside via the sapphire glass plate and the plate member holding portion, and it is therefore possible to reduce the temperature rise and flexion of the polarizer.
Furthermore, the sapphire glass plate and the plate member holding portion are preferably bonded by an adhesive agent. This brings the sapphire glass plate and the plate member holding portion into face-to-face contact, and heat can therefore be transferred from the sapphire glass plate to the plate member holding portion more efficiently.
The sapphire glass plate may preferably be held in a state such that a space in which air can flow exists in at least a part of both surfaces of the sapphire glass plate. This can radiate heat from both surfaces of the sapphire glass plate by the heat transfer due to airflow, and it is possible to reduce the temperature rise and the flexion of the polarizer more efficiently.
A device in accordance with another
Takezawa Takeshi
Watanabe Nobuo
Yamakawa Hidemasa
Adams Russell
Cruz Magda
Oliff & Berridg,e PLC
Seiko Epson Corporation
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