A new solution for the director relaxation problem in twisted nematic film based on wavelet analysis.

The present research considers and explains the application of the Haar wavelets as basis functions in solution of the propagation of perturbations in low-dimensional anisotropic media. The computations of the relaxation problem in the form of traveling waves have shown that the present approach possesses several advantages over regular methods

Synthesis and carbon-13 NMR studies of liquid crystals.

Eight series of liquid crystals containing an electron-donating group at one end of a conjugated system and an electron-withdrawing group at the other end have been synthesized. The electron-donating group is 4- n-alkylpiperazinyl group, the electron-withdrawing group is nitro group and the conjugated system is diphenyldiazene with zero, one or two substituents on the phenyl rings. The substituents are -F, -Cl, and -CH3. Two series of compounds with cyano group as electron-withdrawing group were also synthesized. Most of the compounds synthesized are nematogenic and exhibit rather broad liquid crystalline ranges. The effects of the lateral substituents on the optical absorption and phase transition temperatures are correlated with their nature and position of substitution. Birefringence, dielectric anisotropy, elastic constant ratio and rise time of the liquid crystals were carried out using 10 wt% LC mixtures in E7. It has been found that lateral substituents have subtle effects on the properties. The presence of lateral substituents depresses melting points and clearing points of the liquid crystals. All the liquid crystals synthesized in this work have relatively large values of birefiringence, although the dielectric anisotropy values were not as high as desired. The incorporation of a fluorine atom onto the position neighboring the nitro group enhances the conjugation of the push-pull system and liquid crystals with better physical properties were obtained.The orientation of different segments of 4'-cyanophenyl 4-heptylbenzoate (7CPB) has been investigated using 13C NMR. The method of proton encoded local field (PELF) spectroscopy was used in combination with off-magic-angle spinning (OMAS) of the sample. High-resolution 2D spectra were obtained and the order parameters were calculated from the spectra. Linear relationships between the obtained order parameters and anisotropic chemical shifts determined by 1D 13C NMR were established and semi-empirical parameters were obtained. A 1:2 mixture of 7CPB and its chain-perfluorinated analog (7PFCPB) shows interesting phase behavior with changing of temperature. The mixture was studied by the use of 13C NMR and polarizing optical microscopy. The order parameters of 7CPB in the smectic A phase of the mixture were calculated using the semi-empirical parameters obtained by the 2D NMR method

Adaptive micro-optical phase modulators based on liquid crystal technology

Mención Internacional en el título de doctorThis thesis began with the project “Advanced Devices of Liquid Crystal and Electroluminescent Organic Diodes. Hybrid Applications for 3D Vision” funded by the Spanish government. The goal of this project was the development of optical devices to achieve 3D vision in portable devices without glasses or external elements. In order to achieve the goals of this project, solutions based on liquid crystal are considered. Specifically, adaptive micro-optical phase modulators based on liquid crystal technology are researched in depth. The gradient of the refractive index varies spatially the phase delay experienced by an impinging wavefront of a light beam. By using this effect, any refractive optical element may be reproduced with the proper voltage gradient applied to the sample. This is the main operating principle of the micro-optical phase modulators proposed in this thesis. As original contribution of this thesis, a novel algorithm to solve the position of a nematic liquid crystal molecular director is proposed. Once the liquid crystal is completely characterized, the developing of a specific model to know the electro-optic response of the micro-optical phase modulators is also relevant. Another original contribution is a novel equivalent electric circuit for modeling liquid crystal microlenses. An interesting feature of the model is that it provides an analytical solution for microlenses with modal and hole-patterned electrode schemes, by using a simple software tool. The required driving scheme (modal or hole-patterned) can be predicted. These theories have been validated by experimental results. For more complex devices, the equations are solved by Finite Element Method. A new manufacturing protocol is proposed to make the first set of modal microlens arrays. As a first step simple devices (monopixel cells) are fabricated in order to do a complete study of the liquid crystal electro-optical behavior. The characterization of the liquid crystal electro-optical parameters is determinant in order to design more complex devices. Refractive index and permittivity are the most important features considered. These parameters have been characterized to validate the proposed theoretical modelling of the liquid crystal molecular position. These devices have required special fabrication processes as well as a special characterization set-up especially in terms of size resolution or arrangement complexity. A custom micropositioner is developed and control software is programmed in relation to these tasks. The software automates the characterization process giving directly measured results of: phase modulation, focal distance, thickness or aberrations. These results have made it possible to validate experimentally the proposed electrical modeling for micro-optical devices. Demonstration of the viability of the liquid crystal lenticular technology has been carried out for an autostereoscopic application. This scheme provides the observer with the option of changing between horizontal and vertical views through his portable autostereoscopic display. Finally, last research contributions of this work of thesis have taken advantage of the deep knowledge of the electro-optical properties of lenticular devices for autostereoscopic applications, to guide the design of refined micro-optical phase modulators. Adaptive axicons and optical vortices are specially emphasized because their relevance from both, the scientific and technological point of view.Esta tesis se inició con el proyecto de investigación “Dispositivos avanzados de cristal líquido y diodos orgánicos electroluminiscentes. Aplicaciones híbridas para visión 3D”, financiado por el gobierno español. El objetivo de este proyecto consistía en el desarrollo de dispositivos ópticos para lograr visión 3D en dispositivos portátiles sin necesidad de gafas o elementos externos. Con el fin de alcanzar los objetivos de este proyecto, se consideran soluciones basadas en cristal líquido. En concreto, moduladores adaptativos de fase micro-ópticos basados en tecnología de cristal líquido. El gradiente del índice de refracción varía espacialmente el retardo de fase experimentado por un frente de onda incidente. Mediante el uso de este efecto, cualquier elemento óptico refractivo puede ser reproducido mediante un gradiente de tensión adecuado aplicado a la muestra. Este es el principio de funcionamiento de los moduladores de fase micro-ópticos propuestos en esta tesis. Como aportación original de esta tesis, se propone un nuevo algoritmo para resolver el director molecular de un cristal líquido nemático. Una vez que el cristal líquido está completamente caracterizado, es necesario el desarrollo de un modelo específico para saber la respuesta electro-óptica de los moduladores de fase micro-ópticos. Otra contribución original, consiste en un circuito eléctrico equivalente para el modelado de microlentes de cristal líquido. Una característica interesante del modelo es que proporciona una solución analítica para microlentes con esquemas de electrodos modales y “hole patterned”. Se puede predecir la topología necesaria en función de los parámetros de construcción. Estas teorías han sido validadas por resultados experimentales. Para los dispositivos más complejos, las ecuaciones se resuelven por el método de elementos finitos. Se propone un nuevo protocolo de fabricación para hacer microlentes modales. Como primer paso se fabrican dispositivos sencillos (células monopixel) con el fin de hacer un estudio completo del comportamiento electro-óptico del cristal líquido. La caracterización de los parámetros electro-ópticos de cristal líquido es determinante para diseñar dispositivos más complejos. El índice de refracción y la permitividad son las características más importantes. Estos parámetros se han caracterizado para validar el modelo teórico de la posición molecular de cristal líquido. Estos dispositivos han requerido procesos de fabricación complejos, así como montajes de caracterización determinados. Se ha desarrollado un microposicionador y un software de control. El software automatiza el proceso de caracterización dando resultados de: modulación de fase, distancia focal, grosor o aberraciones. Estos resultados han permitido validar experimentalmente el modelado eléctrico propuesto para dispositivos micro-ópticos. La demostración de la viabilidad de la tecnología propuesta se ha llevado a cabo mediante un dispositivo autoestereoscópico. Este dispositivo ofrece al observador la opción de cambiar entre vistas horizontal y vertical a través de su pantalla autoestereoscópica portátil. Finalmente, los últimos aportes de investigación de este trabajo de tesis se han aprovechado del profundo conocimiento de las propiedades electro-ópticas de los dispositivos lenticulares para aplicaciones autoestereoscópicas. Se pueden destacar los axicones adaptativos y vórtices ópticos por su relevancia tanto desde el punto de vista científico como tecnológico.Este trabajo ha sido desarrollado en el marco de los proyectos TEC2009-13991-C02-01 financiado por el Ministerio de Ciencia e Innovación y FACTOTEM2 S2009/ESP-1781 financiado por la Comunidad de Madrid.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Ignacio Raúl Matías Maestro.- Secretario: Antonia Isabel Pérez Garcilópez.- Vocal: Dimitrios C. Zografopoulo

The modelling of nematic liquid crystal phase devices

The implementation of nematic liquid crystal optical devices, which exploit the voltage dependent, optical path length modification of the electrical Freedrichsz transition, is presented. By combining refractive elements in a diffractive zone structure, efficient and flexible devices with relatively high refractive powers can be constructed. Continuously variable optical properties can be achieved by scaling the optical profile of the refractive elements and applying a phase correction to ensure that the transition between adjacent zones is an integral number of wavelength, hence a continuous optical profile is constructed. Two such devices are postulated; a variable deflection angle prism and a variable focal length lens, though the approach may be extended to other devices. The zones are addressed through combed electrode structures. The required voltage profile is produced by dropping the applied voltages across a shaped conductive strip. A sampling of the profile is transported along the length of the zone via discrete electrodes. In order to produce the required scalability and independent phase correction of the optical profile, it is necessary to restrict the design and operation of the electrodes to the approximately linear region of the response curve. Two-dimensional optical structures can either be achieved through the use of planar earth plates, to mask connections to the centre of the device, or by cascading devices with electrode structures open to connection at the edges. In order to predict the optical profiles of these and other devices, a model was constructed which describes the director orientation through a two-dimensioned electrode structure. The variational finite element method was employed to minimize the electrical Gibbs free energy of a liquid crystal cell, in order to find the equilibrium director orientation. A preliminary version of this model is presented which is restricted to rotation of the liquid crystal to within the plane of the solution

Dynamic Plasmonic Metasurfaces in the Visible Spectrum

As visual display technologies move closer to producing true three dimensional displays, pixel technologies need to be ever smaller and more functional to keep pushing the boundaries. Plasmonic metasurfaces have been shown to control the phase, amplitude and/or polarisation of incoming electromagnetic radiation. Nano-fabrication advancements have resulted in the fabrication of the building blocks of such metasurfaces at nano-scale dimensions, allowing the surfaces to interact with visible light, opening up applications in visual displays. As pixel sizes shrink, smaller colour filters will be required. The excitation of plasmonic resonances in metallic nano-structure arrays have resulted in colour filters an order of magnitude smaller than what is currently commercially available. As colour filters, plasmonic metasurfaces offer numerous advantages over pigment-based colour filters used in modern commercial liquid crystal (LC) displays, including environmental, size and longevity factors. Furthermore, exploiting the wavelength and polarisation dependant scattering of nano-structures, optical components, including lenses, waveplates and holograms containing sub-wavelength pixels have been demonstrated in the visible wavelength spectrum. The metasurfaces are able to mould optical wavefronts into arbitrary shapes with sub-wavelength resolution by introducing spatial variations in the optical response of the light scatterers. The applications demonstrated so far are, on the whole, static devices, that is to say their optical properties may not be altered post fabrication. To realise the full potential of plasmonic metasurfaces to visual applications the devices must be made active. By activating structural colour surfaces, not only may pixel densities potentially be increased simply by removing the need for separate red, green and blue filters, but a new class of high definition ultra-thin display devices may be accessible, whilst the dynamic manipulation of the wavelength and polarisation properties of nano-scattering elements would open up the possibilities to create sub-wavelength holographic pixels. This thesis investigates ways to activate static metasurfaces for colour, flat optic, and holographic applications. First, methods of dynamic control of the structural colour of plasmonic nano-hole arrays are investigated. By combining nano-hole arrays with liquid crystals, transmissive electrically tunable LC-nanohole pixels operating across the visible spectrum with un-polarised input light are experimentally demonstrated. An output analyser in combination with a nematic LC layer enables pixel colour to be electronically controlled through an applied voltage across the device, where LC re-orientation leads to tunable mixing of the relative contributions from the plasmonic colour input. Furthermore, exploiting the strong surface anchoring effects between an aluminium surface and LC molecules a twisted nematic LC cell, using a metallic grating as a combined colour filter, electrode and alignment layer, was shown to act a variable amplitude colour filter. The colour of these pixels was improved greatly utilising a grating-insulator-grating structure unique to this work. Second, a new process for fabricating aluminium nano-rod structures embedded in an elastomeric medium, with high spatial accuracy, is presented. The process is used to create nano-rod plasmonic resonator arrays whose optical properties may be altered by mechanical deformation. The pattern transfer process is further utilised to create dynamic optical elements, including nano-rod arrays for colour filters, tunable focal length Fresnel zone plates and photon sieves, and stretchable holograms with dynamic replay fields.EPSRC David and Susan Hibbitt Scholarshi

A study of optical propagation in polymer liquid crystal nanocomposites for photolithography applications

Technology devices today are rapidly growing in complexity while shrinking in physical size as exemplified by the ultra slim laptops and music players currently available on the market. With the downsizing of packaging and the increase in components, innovative new lithography techniques designed to push the density limit of the digital functions on a chip are becoming more available. Though many di erent forms of lithography exist, all with individual benefits, there currently exists no photolithography tool that can completely eliminate alignment error over a series of exposures; a tool that can bring the industry into the next phase of nanometer photo-patterning. The device that can achieve this goal is designed using digitally adaptable polymer light-valve films to spatially control exposure transmission creating a photomask with an arbitrary and dynamically adjustable pattern.This thesis presents the fundamental engineering behind the design of this novel photomasking application that uses a nanostructured composite. The material used is holographically-formed polymer-dispersed liquid crystal (H-PDLC) film and it is a photosensitive material formed with an interference pattern to contain layers of liquid crystal molecules held in a polymer matrix. With control over individual regions of film in a patterned electrode configuration, areas can be user defined as opaque or transmissive to resist exposing light. When used in a photomasking application, the light and dark fields can be real-time adjusted for rapid mask debugging, mask testing, and multiple exposures with no realignment. To truly understand the microscopic optical behavior of this device, aspects of propagation through the nanostructured film are investigated. Diffractive and edge interference effects are simulated and measured. In addition to this study, transmissive wavefront, scattering, coherence, intensity, and absorption are examined to assess factors limiting imaging due to transmission through the nanostructured thin film. To this point, there have been no investigations into imaging through an H-PDLC as it pertains to patterning photoresist, and limited studies regarding optical propagation within the film. Shown in this work is compelling evidence not only of the practicality of a liquid crystal adaptable photomask but also a study of the optical transmission properties within this type of thin film.Ph.D., Electrical Engineering -- Drexel University, 200

NASA Tech Briefs, September 2008

Topics covered include: Nanotip Carpets as Antireflection Surfaces; Nano-Engineered Catalysts for Direct Methanol Fuel Cells; Capillography of Mats of Nanofibers; Directed Growth of Carbon Nanotubes Across Gaps; High-Voltage, Asymmetric-Waveform Generator; Magic-T Junction Using Microstrip/Slotline Transitions; On-Wafer Measurement of a Silicon-Based CMOS VCO at 324 GHz; Group-III Nitride Field Emitters; HEMT Amplifiers and Equipment for their On-Wafer Testing; Thermal Spray Formation of Polymer Coatings; Improved Gas Filling and Sealing of an HC-PCF; Making More-Complex Molecules Using Superthermal Atom/Molecule Collisions; Nematic Cells for Digital Light Deflection; Improved Silica Aerogel Composite Materials; Microgravity, Mesh-Crawling Legged Robots; Advanced Active-Magnetic-Bearing Thrust- Measurement System; Thermally Actuated Hydraulic Pumps; A New, Highly Improved Two-Cycle Engine; Flexible Structural-Health-Monitoring Sheets; Alignment Pins for Assembling and Disassembling Structures; Purifying Nucleic Acids from Samples of Extremely Low Biomass; Adjustable-Viewing-Angle Endoscopic Tool for Skull Base and Brain Surgery; UV-Resistant Non-Spore-Forming Bacteria From Spacecraft-Assembly Facilities; Hard-X-Ray/Soft-Gamma-Ray Imaging Sensor Assembly for Astronomy; Simplified Modeling of Oxidation of Hydrocarbons; Near-Field Spectroscopy with Nanoparticles Deposited by AFM; Light Collimator and Monitor for a Spectroradiometer; Hyperspectral Fluorescence and Reflectance Imaging Instrument; Improving the Optical Quality Factor of the WGM Resonator; Ultra-Stable Beacon Source for Laboratory Testing of Optical Tracking; Transmissive Diffractive Optical Element Solar Concentrators; Delaying Trains of Short Light Pulses in WGM Resonators; Toward Better Modeling of Supercritical Turbulent Mixing; JPEG 2000 Encoding with Perceptual Distortion Control; Intelligent Integrated Health Management for a System of Systems; Delay Banking for Managing Air Traffic; and Spline-Based Smoothing of Airfoil Curvatures