Optics for a single-lens video projector with color-specific polarization channels

• US 5,374,968 A
• Filed: 11/08/1993
• Issued: 12/20/1994
• Est. Priority Date: 11/08/1993
• Status: Expired due to Fees

• Current Assignee: Transamerica Business Credit Corporation (Aegon Ltd.)
• Original Assignee: Greyhawk Systems, Inc.
• Inventors: Harrison, Douglas H., Haven, Duane A., Vollmer, David W.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Dowling, William C.
• Application Number:
  US08/148,479
• Time in Patent Office: 407 Days
• Field of Search: 353/31, 353/33, 353/34, 353/37, 353/98, 353/20, 348/756, 348/757, 348/779, 348/780, 348/781, 348/782, 359/40
• US Class Current: 353/31
• 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
• CPC Class Codes: H04N 9/3167 for polarizing the light beam polarizing optical systems per se G02B27/28

Abstract

A high-efficiency optical system for use in a liquid-crystal light-valve video projector. High intensity, unpolarized white light is separated into primary color components by color-selective filters transmitting light containing both first and second polarization states. Light of each primary color is characterized by a wavelength passband whereby the endpoints of the passband are defined by first and second wavelengths. The second passband endpoint of the first polarization state of the first primary color overlaps the first passband endpoint of the second polarization state of the second primary color, and the second passband endpoint of the second polarization state of the second primary color overlaps the first passband endpoint of the first polarization state of the third primary color. In addition, the video projector design utilizes low f/# optics in conjunction with absorptive polarizers to remove residual light of an unwanted polarization state allowed into the system by the low f/# optics. This allows high brightness with high efficiency and without sacrificing contrast.

Claims

1. A video projector for producing a full color video image from three separate color channels each of said channels including a polarization modulating light valve, said projector comprising:

a source of white light;

a first optical color channel carrying light of a first color passband and being of a first polarization state, said first color passband encompassing the relatively long wavelengths in said color image;

a second optical color channel carrying light of a second color passband and being of said first polarization state, said second color passband encompassing the relatively short wavelengths in said color image;

a third optical color channel carrying light of a third color passband and being of a second polarization state, said third color passband overlapping at least one of said first or second passbands;

combining means for combining the images from said first, second and third color channels into a composite image; and

projection means for projecting said composite image onto an image plane.

2. The video projector of claim 1 wherein said third color passband overlaps both said first and said second color passbands.

3. The video projector of claim 1 wherein said light valve is a liquid crystal light valve.

4. The video projector of claim 3 wherein said light valve is a reflective liquid crystal light valve.

5. The video projector of claim 1 wherein at least one color channel has an absorbing sheet polarizer therein.

6. The video projector of claim 1 wherein the f/# of said projector is no greater than 5.

7. A video projector for producing a full color video image from separate red, green and blue color channels, comprising:

a source of white light;

a first dichroic filter positioned to receive said white light and adapted to isolate and direct light of a first color into a first primary color channel and the remaining light into a channel containing the remainder of said color spectrum;

a second dichroic filter positioned to receive light from said first dichroic filter, and adapted to isolate a second primary color and direct it into a second primary color channel and the remaining light into a third primary color channel;

first, second and third absorptive sheet polarizers, one positioned in each of said primary color channels and adapted to absorb light in a preferred polarization state and to pass all other light;

first, second and third polarizing prisms, one positioned in each of said primary color channels;

first, second and third polarization modulating light valves, one positioned in each of said primary color channels;

combining means for combining the images from said first, second and third color channels into a composite image; and

projection means for projecting said composite image onto an image plane.

8. The video projector of claim 7, wherein the f/# of the optics thereof is no greater than 5.

9. The video projector of claim 7, wherein said light valves are liquid crystal light valves addressed by cathode ray tubes.

10. The video projector of claim 7 further characterized by the addition of polarization shifting means for rotating the polarization of light impinging thereon by 90°

to one or more of said primary color channels whereby the polarization state of said green channel is different than the polarization state of said red and blue channel.

11. A video projector comprising:

a source of projection light containing substantially the entire visible spectrum;

a reflector of substantially elliptical shape positioned to capture a portion of the light from said projection light source and to reflect said light at a focal point;

a condensing lens positioned beyond the focal point of said reflector and intercepting substantially all of the reflected light from said reflector, said condensing lens adapted to form a first light beam;

a first dichroic beam splitter positioned in the optical path of said first light beam and adapted to divide said first light beam into a second light beam containing a single primary color and a third light beam containing the remaining primary colors;

a first sheet polarizer positioned in the optical path of said second light beam and adapted to transmit a substantial portion of said second beam with an S-polarization state and absorb a substantial portion of light in said second light beam with a P-polarization state;

a first polarization modulator positioned to receive said second light beam and adapted to modulate the polarity thereof with signal information;

a first polarizer-analyzer positioned in the optical path of said second light beam between said first sheet polarizer and said first polarization modulator and adapted to relay light in an S-polarization state only onto said first polarization modulator and to analyze said light beam reflected from said first polarization modulator such that said second light beam reflected from said first polarizer analyzer is amplitude modulated;

a first wave plate positioned in the optical path of said third light beam subsequent to said first dichroic beam splitter, said first wave plate adapted to cause the energy in said P-polarization state to become S-polarized and the energy in said S-polarization state to become P-polarized;

a second dichroic beam splitter positioned to receive said third light beam from said first wave plate and adapted to divide said third light beam into a fourth light beam containing only one of said remaining primary colors and a fifth light beam containing the final primary color;

a second polarization modulator positioned to receive said fourth light beam and adapted to modulate the polarity thereof with signal information;

a second polarizer-analyzer positioned in the optical path of said fourth light beam between said second dichroic filter and said second polarization modulator and adapted to relay light in a P-polarization state only onto said second polarization modulator and to analyze said fourth reflected light beam reflected from said second polarization modulator such that said fourth light beam reflected from said first polarizer analyzer is amplitude modulated;

a second sheet polarizer positioned in the optical path of said fourth light beam subsequent to said second polarizer-analyzer and adapted to transmit a substantial portion of said second beam with an S- polarization state and absorb a substantial portion of light in said second light beam with a P polarization state;

a second wave plate positioned in the optical path of said fourth light beam subsequent to said second polarizer-analyzer, said second wave plate adapted to cause the energy in said S-polarization state to become P-polarized;

a third sheet polarizer positioned in the optical path of said fifth light beam subsequent to said second dichroic filter and adapted to transmit a substantial portion of said fifth beam with an S- polarization state and absorb a substantial portion of light in said fifth light beam with a P-polarization state;

a third polarization modulator positioned to receive said fifth light beam and adapted to modulate the polarity of said beam with signal information;

a third polarizer-analyzer positioned in the optical path of said fifth light beam between third sheet polarizer and said third polarization modulator and adapted to relay light in an S-polarization state only onto said third polarization modulator and to analyze said fifth reflected light beam reflected from said third polarization modulator such that said fifth light beam reflected from said third polarization modulator is amplitude modulated;

a third wave plate positioned in the optical path of said fifth light beam subsequent to said third polarizer-analyzer, said third wave plate adapted to cause the energy in said P-polarization state to become S-polarized;

a first beam combiner positioned in the optical paths of said fourth and fifth light beams and adapted to combine said fourth and fifth light beams into a sixth light beam that contains all of the information of said fourth and fifth light beams;

a second beam combiner positioned in the optical path of said second and sixth light beams and adapted to combine said second and sixth light beams into an seventh light beam contain all of the information in said second and sixth light beams; and

a projection lens positioned in the optical path of said seventh light beam and adapted to focus said beam onto a projection plane.