Cholesteric polarizer for liquid crystal display and overhead projector

A display device adapted to display color images, comprising:

• first, second and third circular polarizers which pass circularly polarized light in a bandwidth within the visible spectrum, each of said polarizers being generally planar;
• first, second and third addressable, liquid crystal cells for selectively modulating the phase of linearly polarized light;
• first, second, third, fourth and fifth quarter-wave plates for converting circularly polarized light into linearly polarized light, each of said quarter-wave plates being generally planar;
• lens means for collecting and collimating light;
• said first circular polarizer being interposed between said lens means and said first liquid crystal cell, and tuned to circularly polarize light of a first primary color;
• said first quarter-wave plate being interposed between said first circular polarizer and said first liquid crystal cell;
• said first liquid crystal cell being tuned to selectively rotate linearly polarized light of said first primary color;
• said second circular polarizer being interposed between said first and second liquid crystal cells, and tuned to circularly polarize light of said first primary color and of a second primary color;
• said second quarter-wave plate being interposed between said second circular polarizer and said first liquid crystal cell;
• said third quarter-wave plate being interposed between said second circular polarizer and said second liquid crystal cell;
• said second liquid crystal cell being tuned to selectively rotate linearly polarized light of said second primary color;
• said third circular polarizer being interposed between said second and third liquid crystal cells, and tuned to circularly polarize light of said second primary color and of a third primary color;
• said fourth quarter-wave plate being interposed between said third circular polarizer and said second liquid crystal cell;
• said fifth quarter-wave plate being interposed between said third circular polarizer and said third liquid crystal cell;
• said third liquid crystal cell being tuned to selectively rotate linearly polarized light of said third primary color;
• and
• analyzer means for rendering visible modulated light exiting said third liquid crystal cell.

A display device adapted to display color images, comprising:

• first, second and third circular polarizers for passing circularly polarized light in a bandwidth within the visible spectrum, each of said polarizers being generally planar;
• first, second and third addressable, liquid crystal cells for selectively modulating the phase of linearly polarized light;
• first, second, third, fourth and fifth quarter-wave plates for converting circularly polarized light into linearly polarized light, each of said quarter-wave plates being generally planar;
• lens means for collecting and collimating light;
• said first circular polarizer being interposed between said lens means and said first liquid crystal cell, and tuned to circularly polarize light of a first primary color and a second primary color;
• said first quarter-wave plate being interposed between said first circular polarizer and said first liquid crystal cell;
• said first liquid crystal cell being tuned to selectively rotate linearly polarized light of said first primary color;
• said second circular polarizer being interposed between said first and second liquid crystal cells, and tuned to circularly polarize light of said first primary color and of a third primary color;
• said second quarter-wave plate being interposed between said second circular polarizer and said first liquid crystal cell;
• said third quarter-wave plate being interposed between said second circular polarizer and said second liquid crystal cell;
• said second liquid crystal cell being tuned to selectively rotate linearly polarized light of said second primary color;
• said third circular polarizer being interposed between said second and third liquid crystal cells, and tuned to circularly polarize light of said second and third primary colors;
• said fourth quarter-wave plate being interposed between said third circular polarizer and said second liquid crystal cell;
• said fifth quarter-wave plate being interposed between said third circular polarizer and said third liquid crystal cell;
• said third liquid crystal cell being tuned to selectively rotate linearly polarized light of said third primary color;
• and
• analyzer means for rendering visible modulated light exiting said third liquid crystal cell.

An overhead projector having high output polarized light, comprising:

• a base having a stage area;
• a projector head mounted to said base, proximate said stage area;
• a light source in said base;
• means for directing light from said light source to said stage area, defining an optical path;
• means for reflecting light, said light reflecting means located adjacent said light source and opposite said stage area with respect to said optical path;
• first lens means for collecting and collimating light from said light source toward said stage area;
• second lens means, interposed between said first lens means and said stage area, for condensing light from said first lens means and directing it through said stage area toward said projector head;
• polarizer means, located between said first and second lens means, for passing light of a first polarization, and for reflecting light of a second polarization;
• and
• means for removing said polarizer means from said base.