Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2000-07-12
2001-06-12
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S627000, C359S485050, C349S194000, C353S034000
Reexamination Certificate
active
06246506
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to optical display devices and more particularly to an optical display device that uses a light valve such as an optical projector for projecting an image on a screen by means of a spatially modulated optical beam produced by a light valve. Further, the present invention relates also to a direct-view-type liquid crystal display device.
An optical projector is a device for projecting images on a screen by means of a spatially modulated optical beam produced by a light valve. In order to improve the visibility of the projected image, intensive efforts are being made to increase the luminance of the optical projectors. In conventional optical projectors, a luminance of about 600 lumens has been required on the screen. Recently, however, there are demands for a luminance of as much as 1000-1200 lumens on the screen.
In order to meet the demand, recent optical projectors tend to use a high-power metal-halide lamp of 350 W or more as compared with conventional optical projectors that typically use a metal-halide lamp of 250 W.
On the other hand, the use of such a high-power optical source causes a problem of severe heating of a polarizer used in the-optical projector in combination with the light valve for producing a linearly polarized optical beam. For example, the polarizer surface is exposed to a luminance of as much as 200 million luxes in such high-power optical projectors. This value of luminance is twice as large as the luminance in a conventional optical projector.
A conventional optical projector typically has a construction that includes a metal-halide lamp as an optical source for producing an optical beam, a polarizer provided in a path of the optical beam for polarizing the incident optical beam to produce a linearly polarized optical beam, a light valve disposed in an optical path of the linearly polarized optical beam for a spatial modulation thereof, an analyzer disposed in an optical path of the spatially modulated optical beam to complete the optical spatial modulation, and a projection lens that projects the output optical beam exiting the analyzer on a screen. The polarizer typically includes dye molecules or iodine molecules dispersed in a polymer matrix and absorbs polarization components in the optical beam except for the component that has a polarization plane perpendicular to an absorption axis of the polarizer.
The optical beam components thus absorbed by the polarizer naturally induce a temperature rise in the polarizer itself, and because of this, conventional optical projectors have used a bulky cooling mechanism for cooling the polarizer as an indispensable element thereof. In a typical example, such a cooling mechanism is used for suppressing the temperature of the polarizer below about 70° C. for the polarizers that use dye molecules. In the case of iodine polarizers, the temperature has to be suppressed below about 60° C. As already noted, the luminance reaches as much as 200 million luxes at the polarizer surface when the metal-halide lamp of 350 W is used in place of the metal-halide lamp of 250 W. Thus, the temperature of the polarizer easily exceeds the foregoing tolerable limit as a result of the absorption of about one-half the energy of the foregoing 200 million luxes when the polarizer is not properly cooled.
Thus, the use of a cooling mechanism has been indispensable in conventional optical projectors for cooling the polarizer. However, such a use of the cooling mechanism inevitably increases the size as well as the cost of the optical projector.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a novel and useful optical projector wherein the foregoing problems are successfully eliminated.
Another and more specific object of the present invention is to provide an optical projector capable of effectively suppressing a temperature rise of a polarizer used in the optical projector for polarizing a high-power optical beam produced by a high-power optical source.
Another object of the present invention is to provide an optical projector that uses a polarizer in combination with an optical source for producing a polarized optical beam, wherein the polarizer reflects an incident optical beam from the optical source except for an optical component having a predetermined polarization plane when producing a polarized optical beam.
Another object of the present invention is to provide an optical projector that uses a reflection-type polarizer in combination with an optical source for producing a polarized optical beam, wherein the problem of projection of a stray light, caused by the reflection of the optical beam at the reflection-type polarizer, on the screen is successfully minimized.
Another object of the present invention is to provide an optical projector that uses a reflection-type polarizer in combination with an optical source for producing a polarized optical beam, wherein the reflected polarization component is processed in a polarization processor for converting the polarization plane thereof so as to be coincident to the polarization plane of the polarization component passed through the reflection-type polarizer.
Another object of the present invention is to provide a polarization device for polarizing an incident optical beam, comprising:
a first polarization element passing a predetermined polarization component included in said incident optical beam and having a predetermined polarization plane, said first polarization element reflecting other polarization components substantially, said other polarization components being included in said incident optical beam and having different polarization planes; and
a second polarization element passing said polarization component having said predetermined polarization plane and absorbing said other polarization components substantially;
said first and second polarization elements being disposed such that a transmission axis of said first polarization element and a transmission axis of said second polarization element coincide with each other;
said first polarization element being disposed at an upstream side of an optical path of said incident optical beam with respect to said second polarization element,
said polarization device further comprising a condenser lens on said optical path at an upstream side of said incident optical beam with respect to said first polarization element.
According to the present invention, about one-half of the energy of the incident optical beam is reflected by the first polarization element without causing a temperature rise in the first or second polarization elements. Further, the second polarization element of the absorption-type refines the polarization of the incident optical beam caused by the first polarization element. By providing a condenser lens on the optical path at the upstream side of the incident optical beam with respect to the first polarization element, the optical path of the polarization component reflected by the first polarization element is offset from the optical path of the optical beam incident to the first polarization element, and the problem of temperature rise of the optical source by the reflected polarization component is avoided.
Another object of the present invention is to provide an optical projector, comprising:
an optical source;
a color separation system disposed on an optical path of an optical beam emitted from said optical source, said color separation system separating said optical beam into respective color optical beams;
a plurality of light valves provided respectively in correspondence to said color optical beams, each of said light valves being disposed on an optical path of a corresponding color optical beam for applying a spatial modulation thereto, said light valve producing thereby a spatially modulated color optical beam;
a plurality of polarization devices respectively provided on said optical paths of said color optical beams incident to said light valves, each of said polarization devices caus
Gotoh Takeshi
Hamada Tetsuya
Kobayashi Tetsuya
Ohashi Noriyuki
Sugawara Mari
Epps Georgia
Fujitsu Limited
Greer Burns & Crain Ltd.
Spector David N.
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