Ultra-efficient Liquid Crystal Projection Displays: Polarizer-free Displays Using Continuous Polarization Gratings.

Abstract

Liquid crystals constitute a distinct state of matter that possesses switchable anisotropic properties. These properties have enabled several electro-optic applications that are compact, and consume low power. The success of the Liquid Crystal Display industry over the past few decades is attributed to these advantages. As a result, today we ﬠnd LCDs in a variety of consumer electronics including cell phones, flat-panel televisions, and projectors. Even though LCDs today are one of the most power efficient display devices, there is still room for improvement. Current LCD designs use polarizers that limit the maximum light efficiency to less than 50%. Due to this a family of polarization independent liquid crystal diffraction gratings has been investigated for projection systems. However the nature of the gratings investigated, and problems associated with their fabrication processes have limited the efficiencies of these elements to much less than those predicted by theory. In this work we mainly discuss one special class of Polarization Gratings (PGs) that has several compelling properties in this context. We develop a solid theoretical framework based on Elastic Continuum principles that reveals several interesting aspects of these devices. Based on this analysis, we lay out foundational design rules that were used to fabricate high quality Liquid Crystal Polarization Gratings (LCPGs) with properties close to those predicted in theory. We then develop new fabrication approaches for creating these gratings on virtually any type of reflective surface; leading to a polarizer free Liquid Crystal On Silicon (LCOS) based projection system that provides a brightness enhancement of nearly two when compared with standard approaches. We then identify and implement an even more revolutionary modulation scheme using polymer-PGs, that achieves the same high efficiency with any off-the-shelf LC microdisplay, and thus can be easily integrated into commercial LC projectors. Key aspects of this technology are discussed and techniques to dramatically enhance contrast ratios are revealed. We conclude with a summary of results, and suggest directions for future research.