Multicolor projector employing diffraction grating type liquid crystal light modulators

• US 5,237,435 A
• Filed: 01/23/1991
• Issued: 08/17/1993
• Est. Priority Date: 01/24/1990
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Oshima, Shigeru, Kurematsu, Katsumi, Minoura, Nobuo
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Duong, Tai V.
• Application Number:
  US07/644,932
• Time in Patent Office: 937 Days
• Field of Search: 359/40-42, 359/48, 359/49, 359/53, 359/94, 359/95, 359/569-574, 359/246, 359/247, 359/249, 359/256, 359/253, 359/278, 359/495, 359/498, 353/31, 353/34, 353/122, 358/61, 358/62, 358/236
• US Class Current: 349/8
• CPC Class Codes: G02F 1/1333 Constructional arrangements; Manufacturing methodsG02F1/135, G02F1/136 take precedence
• CPC Class Codes: G02F 1/133565 inside the LC elements, i.e. between the cell substrates
• CPC Class Codes: G02F 1/292 by controlled diffraction or phased-array beam steering controlled diffraction for optical switching G02F1/31
• CPC Class Codes: H04N 9/3105 for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators simultaneous projection in colour photography G03B33/10; beam splitting or combining systems per se G02B27/10

Abstract

A projector capable of compactizing the structure and improving the efficiency of light utilization is disclosed. The projector has an illuminating system, a light modulation device and a projection optical system. A first and a second lights of mutually different colors are emitted from the illumination optical system. The light modulating device has a first light modulator for modulating the first light according to a first image signal and a second light modulator for modulating the second light according to a second image signal. Each of the first and second light modulators is provided with a grating, a liquid crystal filled in the grooves of the grating and a driver for driving the molecules of the liquid crystal. The driver is adapted to drive the molecules of the liquid crystal in such a manner that the liquid crystal and the grating have mutually substantially matching refractive indexes in a certain state but have mutually unmatched refractive indexes in another state, thereby generating or substantially erasing a diffraction grating by the grating and the liquid crystal. A first and a second images of mutually different colors are projected on a screen by the first and second lights from the first and second light modulators.

Claims

1. A projector comprising

an illumination system including,

a light source emitting a white light,

a conversion system for converting said white light into a polarized light, and

a color separation system for splitting said polarized light into red, green and blue lights for generating first, second and third lights of mutually different colors;

light modulation means including,

a first light modulator for modulating said first light according to a first image,

a second light modulator for modulating said second light according to a second image,

a third light modulator for modulating said third light according to a third image, wherein each of said first, second and third light modulators is provided with a grating including grooves liquid crystal filled in the grooves of said grating and a driver for driving molecules of said liquid crystal, said driver being adapted to drive the molecules of liquid crystal in such a manner that the liquid crystal and the grating have mutually substantially matching refractive indexes in a certain state but have mutually unmatched refractive indexes in another state, thereby generating or substantially erasing a diffraction grating by said grating and said liquid crystal, said first and second light modulators are positioned in a mutually common optical path, different from the optical path in which said third light modulator is positioned, betwen said illuminating system and said projection optical system, are arranged in such a manner that the direction of grooves of said gratings are mutually substantially perpendicular, and are adapted to orient said molecules of the liquid crystal along the grooves of said gratings in said another state;

a projection optical system for projecting a first and second images of mutually different colors by said first and second lights from said first and second light modulators, said projection optical system further adapted to project a third image of a color different from those of said first and second lights, by said third light from said third light modulator, and superposes said third image with said first and second images; and

said illuminating system is adapted to rotate the polarizing plane of one of said first and second lights from said color separation system substantially perpendicularly to the polarizing plane of the other, thereby substantially matching the polarizing plane of the first light with the direction of grooves of said grating of said first light modulator and substantially matching the polarizing plane of said second light with the direction of grooves of said grating of said second light modulator, and direct said first and second lights to said common optical path and said third light to said optical path in which said third light modulator is positioned.

2. A projector according to claim 1, wherein said first and second light modulators are integrally constructed.

3. A projector according to claim 1, wherein said projection optical system comprises a color synthesizing system composed of a single dichroic mirror for synthesizing said modulated first, second and third lights from said first, second and third light modulators.

4. A projector according to claim 1, wherein said illuminating system comprises a 1/2 wavelength plate in the optical path of said first light from said color separation system thereby rotating the polarizing plane of said first light with respect that of said second light, and further comprises an arrangement of a mirror and a polarizing beam splitter thereby directing said second light to said polarizing beam splitter, reflecting said first light from said 1/2 wavelength plate by said mirror to said polarizing beam splitter and directing said first and second lights by said polarizing beam splitter to said common optical path.

5. A projector according to claim 3, wherein said dichroic mirror is adapted to reflect said first and second lights and transmit said third light.

6. A projector according to claim 3, wherein said dichroic mirror is adapted to transmit said first and second lights and reflect said third light.

7. A projector according to claim 1, wherein said first, second and third lights are respectively blue, red and green.

8. A projector comprising:

an illuminating system for emitting first and second lights of mutually different colors and mutually different polarization planes;

light modulation means including a first light modulator for modulating said first light according to a first image signal and a second light modulator for modulating said second light according to a second image signal, wherein each of said first and second light modulators is provided with a grating including grooves, liquid crystal filled in the grooves of said grating, and a driver for driving molecules of said liquid crystal, said driver is adapted to drive the molecules of liquid crystal in such a manner that the liquid crystal and the grating have mutually substantially matching refractive indexes in a certain state but have mutually unmatched refractive indexes in another state, thereby generating or substantially erasing a diffraction grating by said grating and said liquid crystal; and

a projection optical system for projecting first and second images of mutually different colors by said first and second lights from said first and second light modulators, said first and second light modulators are positioned mutually closely in a common optical path and are so arranged that the directions of grooves of said gratings are mutually substantially perpendicular, and said first and second lights have mutually substantially perpendicular polarizing planes. to match with the direction of said grooves of said gratings.

9. A projector according to claim 8, wherein said first and second lights are respectively red and blue.