Reflective liquid crystal display overhead projection system using a reflective linear polarizer and a fresnel lens

• US 5,333,072 A
• Filed: 12/31/1992
• Issued: 07/26/1994
• Est. Priority Date: 12/31/1992
• Status: Expired due to Fees

• Current Assignee: 3M Company
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: Willett, Stephen J.
• Primary Examiner(s): Gross, Anita P.
• Application Number:
  US07/999,089
• Time in Patent Office: 572 Days
• Field of Search: 359/40, 359/41, 359/63, 359/70, 353/122
• US Class Current: 349/6
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G03B 21/132 Overhead projectors, i.e. capable of projecting hand-writing or drawing during action epidiascopic projectors G03B21/08
• CPC Class Codes: H04N 5/7441 the modulator being an array of liquid crystal cells

Abstract

A reflective liquid crystal display overhead projection system. The projection system includes a reflective polarizer, a phase modulating liquid crystal display on the reflective polarizer, and a fresnel lens on the liquid crystal display. Unpolarized light rays are directed toward the fresnel lens, pass through the liquid crystal display, and are reflected and polarized by the reflective polarizer. The light rays then pass back through the liquid crystal display and the fresnel lens and on toward a projector head, where the light rays are analyzed by a polarizer and projected toward a screen.

Claims

1. An optical stack for use in a reflective liquid crystal display projection system comprising a reflective micro-prism array MacNeille polarizer, a phase modulating liquid crystal display provided on the polarizer, and a transmissive fresnel lens provided on the liquid crystal display, wherein unpolarized light rays directed toward the fresnel lens pass through the fresnel lens and the liquid crystal display, are then reflected and polarized by the polarizer, pass back through the liquid crystal display where the phase of the light rays is modulated, and pass back through the fresnel lens.

2. A reflective liquid crystal display overhead projection system, comprising:

a first linear polarizer which is a reflective micro-prism array MacNeille polarizer;

a phase modulating liquid crystal display provided on the first linear polarizer;

a transmissive fresnel lens provided on the liquid crystal display;

a second linear polarizer; and

a projector head, wherein the second linear polarizer is attached to the projector head, and wherein the projector head comprises a projector lamp and a projection lens, wherein unpolarized light rays from the lamp are directed toward the fresnel lens, pass through the fresnel lens and the liquid crystal display, are reflected and polarized by the first linear polarizer, pass back through the liquid crystal display where the phase of the light rays is modulated, pass back through the fresnel lens, and are directed toward and pass through the second linear polarizer and projection lens, whereby an image displayed by the liquid crystal display is projected onto a screen.

3. A reflective liquid crystal display overhead projection system, comprising:

a first linear polarizer which is a reflective polarizer comprised of a circular polarizer and a quarter-wave retarding plate;

a phase modulating liquid crystal display provided on the first linear polarizer;

a transmissive fresnel lens provided on the liquid crystal display;

a second linear polarizer; and

a projector head, wherein the second linear polarizer is attached to the projector head, and wherein the projector head comprises a projector lamp and a projection lens, wherein unpolarized light rays from the lamp are directed toward the fresnel lens, pass through the fresnel lens and the liquid crystal display, are reflected and polarized by the first linear polarizer, pass back through the liquid crystal display where the phase of the light rays is modulated, pass back through the fresnel lens, and are directed toward and pass through the second linear polarizer and projection lens, whereby an image displayed by the liquid crystal display is projected onto a screen.

4. A reflective liquid crystal display overhead projection system, comprising:

a first linear polarizer which is a reflective polarizer;

a phase modulating liquid crystal display provided on the first linear polarizer;

a transmissive fresnel lens provided on the liquid crystal display;

a second linear polarizer comprised of one of a micro-prism array MacNeille polarizer and a birefringent interference polarizer; and

a projector head, wherein the second linear polarizer is attached to the projector head, and wherein the projector head comprises a projector lamp and a projection lens, wherein unpolarized light rays from the lamp are directed toward the fresnel lens, pass through the fresnel lens and the liquid crystal display, are reflected and polarized by the first linear polarizer, pass back through the liquid crystal display where the phase of the light rays is modulated, pass back through the fresnel lens, and are directed toward and pass through the second linear polarizer and projection lens, whereby an image displayed by the liquid crystal display is projected onto a screen.

5. A reflective liquid crystal display overhead projection system, comprising:

a first linear polarizer which is a reflective polarizer;

a phase modulating liquid crystal display provided on the first linear polarizer;

a transmissive fresnel lens provided on the liquid crystal display;

a second linear polarizer comprised of a circular polarizer and a quarter-wave retarding plate; and

a projector head, wherein the second polarizer is attached to the projector head, and wherein the projector head comprises a projector lamp and a projection lens, wherein unpolarized light rays from the lamp are directed toward the fresnel lens, pass through the fresnel lens and the liquid crystal display, are reflected and polarized by the first linear polarizer, pass back through the liquid crystal display where the phase of the light rays is modulated, pass back through the fresnel lens, and are directed toward and pass through the second linear polarizer and projection lens, whereby an image displayed by the liquid crystal display is projected onto a screen.

6. A method of projecting an image displayed by a liquid crystal display onto a screen, comprising:

directing unpolarized light rays toward an optical stack, wherein the optical stack includes a first linear polarizer which is a reflective micro-prism array MacNeille polarizer, a phase modulating liquid crystal display provided on the reflective polarizer, and a transmissive fresnel lens provided on the liquid crystal display, wherein the unpolarized light rays pass through the fresnel lens and the liquid crystal display;

reflecting and polarizing the light rays by the use of the first polarizer, wherein the reflected, polarized light rays pass back through the liquid crystal display and the fresnel lens, and then travel toward a projector head;

analyzing the reflected, polarized light rays with a second linear polarizer attached to the projection head; and

projecting the reflected, polarized light rays onto a projection screen.