Unitary prepolarizing prism assembly for a four color liquid crystal light valve image projector

• US 4,842,374 A
• Filed: 09/23/1988
• Issued: 06/27/1989
• Est. Priority Date: 07/27/1987
• Status: Expired due to Fees

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Ledebuhr, Arno G.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Duong, Tai V.
• Application Number:
  US07/248,464
• Time in Patent Office: 277 Days
• Field of Search: 350/337, 350/342, 350/331 R, 350/174, 350/401, 353/20, 353/31, 353/33, 353/81, 353/84, 353/122, 358/225, 358/226, 358/232, 358/237
• US Class Current: 349/8
• CPC Class Codes: G02F 1/1313 specially adapted for a particular application
• CPC Class Codes: H04N 9/18 using separate electron beams for the primary colour signals H04N9/27 takes precedence

Abstract

A simple, less costly prepolarizing prism assembly for a four color liquid crystal light valve image projector is disclosed. The invention is a unitary assembly which provides a combined beam of light having a first component of a first color and first polarization state and a second component of a second color and a second polarization state. The invention includes a first color filter for reflecting, from an input beam of unpolarized white light, light of a third color and transmitting light of the first and second colors in a combined beam along a first optical path. A first prepolarizer is mounted on the first filter for extracting, from the combined beam, light of a second color and the first polarization state. A second prepolarizer is mounted on the first prepolarizer for extracting, from the combined beam, light of a first color and the second polarization state.

Claims

1. A four color liquid crystal light valve image projector comprising:

a prepolarizing prism assembly for which provides, from an input beam of unpolarized white light, an output beam of light having a first component of a first color and first polarization state and a second component of a second color and a second polarization state, said prepolarizing prism assembly providing a first optical path from an input end to an output end;

a main polarizer disposed to receive said output beam of light from said prepolarizing assembly, said main polarizer directing light of said first color and said first polarization state along a second optical path, said main polarizer directing light of said second color and said second polarization state along a third optical path, said main polarizer receiving polarization-modulated light along said second and third optical paths and directing said polarization-modulated light along a fourth optical path;

liquid crystal light valve means disposed on said second and third optical paths for receiving the light transmitted on said second and third optical paths, said liquid crystal light valve means modulating the polarization state of received light and directing said polarization-modulated light along said second and third optical paths to said main polarizer.

2. A four color liquid crystal light valve image projector as recited in claim 1 wherein said prepolarizing prism assembly comprises:

a color filter for receiving said input beam of unpolarized white light at the input end of said optical path, said color filter reflecting light of a third color away from said optical path, said color filter transmitting light of said first and second colors along said first optical path;

a first prepolarizer disposed on said optical path to receive the light of said first and second colors transmitted from said color filter, said first prepolarizer reflecting received light of said second color and said first polarization state away from said first optical path, said first prepolarizer transmitting the remaining components of said the light received from said color filter along the first optical path;

a second prepolarizer disposed on said first optical path to receive the light transmitted from said first prepolarizer, said second prepolarizer reflecting received light of said first color and said second polarization state away from said first optical path, said second prepolarizer transmitting the remaining components of the light received from said first prepolarizer along said first optical path,

whereby an output beam of light having a first component of a first color and first polarization state and a second component of a second color and a second polarization state is provided at the output end of said first optical path.

3. A four color liquid crystal light valve image projector as recited in claim 2 wherein:

said first prepolarizer is MacNeille biprism;

said second prepolarizing prism is a MacNeille biprism, said second prepolarizing prism being oriented at 90 degrees with respect to the orientation of said first prepolarizing prism.

4. A four color liquid crystal light valve image projector as recited in claim 3 wherein:

said main polarizer is a MacNeille biprism having the same orientation as said second prepolarizer.

5. A four color liquid crystal light valve image projector as recited in claim 4 wherein:

said color filter reflects blue light away from said optical path;

said first prepolarizer reflects green light of said second polarization state away from the first optical path; and

said second prepolarizer reflects red light of said second polarization state away from the first optical path, whereby, red light of said second polarization and green light of said first polarization are transmitted to the output end of said first optical path.

6. A prepolarizing prism assembly for which provides, from an input beam of unpolarized white light, an output beam of light having a first component of a first color and first polarization state and a second component of a second color and a second polarization state, said prepolarizing prism assembly providing an optical path from an input end to an output end, said prepolarizing assembly comprising:

a color filter for receiving said input beam of unpolarized white light at the input end of said optical path, said color filter reflecting light of a third color away from said optical path, said color filter transmitting light of said first and second colors along said optical path;

a first prepolarizer disposed on said optical path to receive the light of said first and second colors transmitted from said color filter, said first prepolarizer reflecting received light of said second color and said first polarization state away from said first optical path, said first prepolarizer transmitting the remaining components of said the light received from said color filter along the optical path;

a second prepolarizer disposed on said optical path to receive the light transmitted from said first prepolarizer, said second prepolarizer reflecting received light of said first color and said second polarization state away from said optical path, said second prepolarizer transmitting the remaining components of the light received from said first prepolarizer along said optical path,

whereby an output beam of light having a first component of a first color and first polarization state and a second component of a second color and a second polarization state is provided at the output end of said optical path.

7. A prepolarizing prism assembly as recited in claim 6 wherein:

said light component of a first color is red light;

said light component of a second color is green light; and

said light of a third color is blue light.

8. A prepolarizing prism assembly as recited in claim 6 wherein:

said first prepolarizer is MacNeille biprism;

said second prepolarizing prism is a MacNeille biprism, said second prepolarizing prism being oriented at 90 degrees with respect to the orientation of said first prepolarizing prism.

9. A prepolarizing prism assembly as recited in claim 8 wherein said color filter is a zero degree filter.

10. A prepolarizing prism assembly as recited in claim 8 wherein:

said color filter reflects blue light away from said optical path;

said first prepolarizer reflects green light of said second polarization state away from the optical path; and

said second prepolarizer reflects red light of said second polarization state away from the optical path, whereby, red light of said second polarization and green light of said first polarization are transmitted to the output end of said optical path.