Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2001-04-25
2002-09-24
Adams, Russell (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S033000, C353S034000, C353S037000, C349S005000, C349S009000, C348S742000
Reexamination Certificate
active
06454416
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal projector, and in particular to a color liquid crystal projector having an improved optical system.
The color liquid crystal projector is such that white light from one light source is split into three primary colors of red (R), green (G) and blue (B), then the three lights of the primary colors are entered into the red-color, green-color and blue-color liquid crystal display panels, respectively, and then the three lights of the primary colors reflected from the respective liquid crystal display panels are recombined and are projected onto a screen via a projection lens.
Conventionally, a means for splitting white light from one light source into three primary-color lights and for splitting and combining the polarized light comprises three polarizing beam splitters for the three primary colors, respectively, and a means for combining the three primary-color lights uses a cross dichroic prism.
SUMMARY OF THE INVENTION
In the liquid crystal projector of the above configuration, the optical system for color splitting and color recombination is large in size, and further, a problem has been pointed out that, because two liquid crystal display panels face toward each other with two of the three polarizing beam splitters and the cross dichroic prism interposed therebetween, the contrast ratio of the combined images is reduced by light reflections between the two opposing liquid crystal display panels.
The present invention has been made in view of the above situations, and therefore it is an object of the present invention to provide a small and lightweight liquid crystal projector. Further, it is another object of the present invention to provide a liquid crystal projector featuring a good contrast ratio.
The following explains briefly an outline of representative ones of the inventions disclosed in this specification.
In accordance with an embodiment of the present invention, there is provided a color liquid crystal projector including an optical system for splitting light from a light source into first primary-color light, second primary-color light and third primary-color light, first, second and third reflection type liquid crystal display panels corresponding to the first primary-color light, the second primary-color light and the third primary-color light, respectively, and a projection lens for projecting the first primary-color light, the second primary-color light and the third primary-color light from the optical system onto a screen, the optical system comprising: a linear polarizer receiving the light from the light source; a mirror for reflecting the first primary-color light in the light from the linear polarizer and transmitting the second primary-color light and the third primary-color light in the light from the linear polarizer; a first phase plate for rotating a direction of polarization of the second primary-color light from the mirror through 90° and transmitting the second primary-color light, and for transmitting the third primary-color light without changing a direction of polarization thereof; a first prism for transmitting the second primary-color light from the first phase plate and then entering the second primary-color light into the second liquid crystal display panel, and reflecting the third primary-color light from the first phase plate and then entering the third primary-color light into the third liquid crystal display panel; a second prism for entering the first primary-color light from the mirror into the first liquid crystal display panel; and a dichroic prism for combining the first primary-color light, the second primary-color light and the third primary-color light reflected from the first, second and third liquid crystal display panels, respectively.
In accordance with another embodiment of the present invention, there is provided a color liquid crystal projector comprising a light source and an optical system for reflecting light from the light source by reflection type liquid crystal display panels and projecting light reflected from the reflection type liquid crystal display panels, the optical system including: a mirror for reflecting a light of a first wavelength of the light from the light source and reflecting lights of second and third wavelengths of the light from the light source; a first phase plate for rotating a direction of polarization of the light of the second wavelength through 90° from the mirror and transmitting the light of the second wavelength, and transmitting the light of the third wavelength without changing a direction of polarization thereof; a first prism for transmitting the light of the second wavelength from the first phase plate and reflecting the light of the third wavelength from the first phase plate; a first reflection type liquid crystal display panel for reflecting the light of the first wavelength from the mirror; a second reflection type liquid crystal display panel for reflecting the light of the second wavelength from the first prism; a third reflection type liquid crystal display panel for reflecting the light of the third wavelength from the first prism; and a dichroic prism for combining lights from the first, second and third reflection type liquid crystal display panels, each of the first, second and third reflection type liquid crystal display panels being provided with reflective electrodes for reflecting light entering a liquid crystal layer thereof.
The liquid crystal projectors of the above configuration are capable of being made smaller in size than the conventional liquid crystal projector requiring a prism for each of the liquid crystal display panels, because the two liquid crystal display panels can be disposed with the above-described prism interposed therebetween.
The mirror is used instead of the prisms, as an element for reflecting a first primary-color light in white light from the light source and transmitting a second primary-color light and a third primary-color light, and consequently, the liquid crystal projector is capable of being made lightweight.
Two of the three required liquid crystal display panels are capable of being disposed at the two sides of the prism perpendicular to each other, respectively, and consequently, they do not need to be disposed to face each other with the prism interposed therebetween. As a result, light incident on one of the three liquid crystal display panels does not enter another of the three liquid crystal display panels, and therefore the display contrast ratio is improved.
REFERENCES:
patent: 6176586 (2001-01-01), Hirose et al.
patent: 6273567 (2001-08-01), Conner et al.
patent: 6309071 (2001-10-01), Huang et al.
Aoto Katsuhide
Yanagawa Kaoru
Adams Russell
Antonelli Terry Stout & Kraus LLP
Koval Melissa
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