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Liquid crystal

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Full-Text Articles in Physics

Low Absorption Liquid Crystal Materials For Midwave Infrared, Amy Creekmore Jan 2015

Low Absorption Liquid Crystal Materials For Midwave Infrared, Amy Creekmore

Electronic Theses and Dissertations

Liquid crystal is an amazing class of soft matters with applications spanning from visible, infrared, millimeter wave, to terahertz. In addition to direct-view displays and projection displays, liquid crystal is also widely used in adaptive optics, tunable-focus lens, and laser beam steering. Although the visible region has well developed materials and mixtures for the vast variety of applications, the midwave infrared (MWIR) region of the electromagnetic spectrum invites much development as only a few materials have been developed with these applications in mind. Unlike visible region, the major challenge for mid-wave infrared liquid crystal is inherently large absorption loss. To ...


Advanced Liquid Crystal Materials For Display And Photonic Applications, Yuan Chen Jan 2014

Advanced Liquid Crystal Materials For Display And Photonic Applications, Yuan Chen

Electronic Theses and Dissertations

Thin-film-transistor (TFT) liquid crystal display (LCD) has been widely used in smartphones, pads, laptops, computer monitors, and large screen televisions, just to name a few. A great deal of effort has been delved into wide viewing angle, high resolution, low power consumption, and vivid color. However, relatively slow response time and low transmittance remain as technical challenges. To improve response time, several approaches have been developed, such as low viscosity liquid crystals, overdrive and undershoot voltage schemes, thin cell gap with a high birefringence liquid crystal, and elevated temperature operation. The state-of-the-art gray-to-gray response time of a nematic LC device ...


Optically Isotropic Liquid Crystals For Display And Photonic Applications, Jin Yan Jan 2013

Optically Isotropic Liquid Crystals For Display And Photonic Applications, Jin Yan

Electronic Theses and Dissertations

For the past few decades, tremendous progress has been made on liquid crystal display (LCD) technologies in terms of stability, resolution, contrast ratio, and viewing angle. The remaining challenge is response time. The state-of-the-art response time of a nematic liquid crystal is a few milliseconds. Faster response time is desirable in order to reduce motion blur and to realize color sequential display using RGB LEDs, which triples the optical efficiency and resolution density. Polymer-stabilized blue phase liquid crystal (PS-BPLC) is a strong candidate for achieving fast response time because its self-assembled cubic structure greatly reduces the coherence length. The response ...


Submillisecond-Response Blue Phase Liquid Crystals For Display Applications, Kuan Ming Chen Jan 2012

Submillisecond-Response Blue Phase Liquid Crystals For Display Applications, Kuan Ming Chen

Electronic Theses and Dissertations

With exploding growth of information exchanges between people, display has become indispensable in our daily lives. After decades of intensive research and development in materials and devices, and massive investment in manufacturing technologies, liquid crystal display (LCD) has overcome various obstacles and achieved the performance we need, such as wide viewing angle, high contrast ratio, and high resolution, etc. These excellent performances make LCD prevailed in every perspective. Recently, with the demands of energy conservation, a greener LCD with lower power consumption is desired. In order to achieve this goal, new energy-effective driving methods, such as field sequential color display ...


Optical Fluid-Based Photonic And Display Devices, Su Xu Jan 2012

Optical Fluid-Based Photonic And Display Devices, Su Xu

Electronic Theses and Dissertations

Conventional solid-state photonic devices exhibit an ultra-high optical performance and durability, but minimal adaptability. Recently, optical fluid-based photonic and display devices are emerging. By dynamically manipulating the optical interface formed by liquids, the optical output can be reconfigured or adaptively tuned in real time. Such devices exhibit some unique characteristics that are not achievable in conventional solid-state photonic devices. Therefore, they open a gateway for new applications, such as image and signal processing, optical communication, sensing, and lab-on-a-chip, etc. Different operation principles of optical fluidbased photonic devices have been proposed, for instance fluidic pressure, electrochemistry, thermal effect, environmentally adaptive hydrogel ...


Fast Response Dual Frequency Liquid Crystal Materials, Qiong Song Jan 2010

Fast Response Dual Frequency Liquid Crystal Materials, Qiong Song

Electronic Theses and Dissertations

Dual frequency liquid crystal (DFLC) exhibits a positive dielectric anisotropy at low frequencies and negative dielectric anisotropy at high frequencies. The frequency where dielectric anisotropy is zero is called crossover frequency. DFLC can achieve fast rise time and fast decay time with the assistance of applied voltage. However, one drawback of DFLC is that it has dielectric heating effect when driven at a high frequency. Thus, the first part of this dissertation is to develop low crossover frequency DFLC materials. The dielectric relaxation and physical properties of some single- and double-ester compounds were investigated. Experimental results indicate that the double-ester ...


Propagation Effect In Inhomogeneous Media, Including Media With Light-Induced And Fixed Gratings, Chang-Ching Tsai Jan 2006

Propagation Effect In Inhomogeneous Media, Including Media With Light-Induced And Fixed Gratings, Chang-Ching Tsai

Electronic Theses and Dissertations

Optical waves propagation in various types of volume gratings, materials with constant impendence and optical fibers are studied. Instability of cross–phase modulation and of Energy transfer via GRON-type (Grating-type Orientational Nonlinearity in Liquid Crystal) Stimulated Scattering is numerically observed. Two diffractive optical elements made of volume gratings are suggested and analyzed. A transmission hologram based on the analogy with Stimulated Raman Adiabatic Passage (STIRAP) in nonlinear optics is proposed. This transmission hologram demonstrates high diffraction efficiency and low sensitivity to polarization and hologram strength. The other is a reflection hologram with two crossed-gratings. It features good angular selectivity in ...


Polarization-Independent Liquid Crystal Devices, Yi-Hsin Lin Jan 2006

Polarization-Independent Liquid Crystal Devices, Yi-Hsin Lin

Electronic Theses and Dissertations

Liquid crystal (LC) devices can be operated as amplitude modulators and phase modulators. LC amplitude modulation is commonly used in liquid crystal display (LCD) while phase-only modulation is useful for laser beam steering, tunable grating, prism, lens, and other photonic devices. Most LC devices are polarization dependent and require at least one polarizer. As a result, the optical efficiency is low. To enhance display brightness, a power hungry backlight has to be used leading to a high power consumption and short battery life. In a LC phase modulator, the polarization dependent property complicates the laser beam steering system. It is ...


Liquid Crystal Materials And Tunable Devices For Optical Communications, Fang Du Jan 2005

Liquid Crystal Materials And Tunable Devices For Optical Communications, Fang Du

Electronic Theses and Dissertations

In this dissertation, liquid crystal materials and devices are investigated in meeting the challenges for photonics and communications applications. The first part deals with polymer-stabilized liquid crystal (PSLC) materials and devices. Three polymer-stabilized liquid crystal systems are developed for optical communications. The second part reports the experimental investigation of a novel liquid-crystal-infiltrated photonic crystal fiber (PCF) and explores its applications in fiber-optic communications. The curing temperature is found to have significant effects on the PSLC performance. The electro-optic properties of nematic polymer network liquid crystal (PNLC) at different curing temperatures are investigated experimentally. At high curing temperature, a high contrast ...


Liquid Crystal Optics For Communications, Signal Processing And 3-D Microscopic Imaging, Sajjad Khan Jan 2005

Liquid Crystal Optics For Communications, Signal Processing And 3-D Microscopic Imaging, Sajjad Khan

Electronic Theses and Dissertations

This dissertation proposes, studies and experimentally demonstrates novel liquid crystal (LC) optics to solve challenging problems in RF and photonic signal processing, freespace and fiber optic communications and microscopic imaging. These include free-space optical scanners for military and optical wireless applications, variable fiber-optic attenuators for optical communications, photonic control techniques for phased array antennas and radar, and 3-D microscopic imaging. At the heart of the applications demonstrated in this thesis are LC devices that are non-pixelated and can be controlled either electrically or optically. Instead of the typical pixel-by-pixel control as is custom in LC devices, the phase profile across ...