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Title: Development of Switchable Polarization Gratings for Highly Efficient Liquid Crystal Displays
Authors: Jones, William Michael
Advisors: Dr. Michael J. Escuti, Committee Chair
Dr. John F. Muth, Committee Member
Dr. Keith R. Weninger, Committee Member
Dr. Chongchang Mao, Committee Member
Dr. Michael J. Escuti, Committee Chair
Dr. John F. Muth, Committee Member
Dr. Keith R. Weninger, Committee Member
Dr. Chongchang Mao, Committee Member
Keywords: liquid crystal
polarization grating
holography
polarized light
Schlieren projection system
liquid crystal
polarization grating
holography
polarized light
Schlieren projection system
Issue Date: 11-Dec-2006
Degree: MS
Discipline: Electrical Engineering
Abstract: Portable displays are now found in an abundance of electronic devices and serve entertainment, educational, and business needs. One technology, the liquid crystal display (LCD), has proven to provide clear images with high contrasts and viewing-angles, and is growing in demand. Projection displays based on high resolution microdisplays are also becoming increasingly popular due to their small size and large image. However, one significant problem with present-day displays is their low optical efficiency. This poor efficiency can be attributed to a variety of causes, including absorption or reflection losses at interfaces, the method to achieve color synthesis, or the fact that they operate on polarized light. As a result, projection devices require battery-draining backlights in order to achieve adequate brightness. Previous researchers have looked to a diffractive element known as a liquid crystal polarization grating (LCPG) to solve this problem, as it was theoretically predicted to modulate unpolarized light, achieve 100% diffraction efficiencies, and possess only three diffraction orders (0, +1, -1). Experimental attempts to realize the useful properties of this liquid crystal device have been promising, but until now have not demonstrated the unique optical properties predicted by theory. This thesis details the successful design and fabrication of LCPGs which, when exposed to monochromatic light, experimentally-possess ˜100% light efficiencies, modulate unpolarized light with an applied voltage, and provide relatively high contrasts (up to 600:1). A LCPG projection display prototype is built based on a Schlieren projection scheme and a color-sequential light engine (with three light-emitting-diodes). Exciting results from this systems are found, including switching times as low as 2ms, threshold electric fields of <1V⁄micrometer, multi-color contrasts as high as 144:1, and etendue on the order of 5-10mmˆ2-sr. Further LCPG projection display development aiming to increase the diffraction angle and match it with reflective silicon substrates will enable a microdisplay technology which combines two desirable properties: high optical efficiency with unpolarized light sources, and strong potential for low-cost, high-yield manufacturing.
URI: http://www.lib.ncsu.edu/resolver/1840.16/2599
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