MSSM soft terms from supergravity with gauged R-symmetry in de Sitter vacuum

We work out the phenomenology of a model of supersymmetry breaking in the presence of a tiny (tunable) positive cosmological constant, proposed by the authors in arXiv:1403.1534. It utilizes a single chiral multiplet with a gauged shift symmetry that can be identified with the string dilaton (or an appropriate compactification modulus). The model is coupled to the MSSM, leading to calculable soft supersymmetry breaking masses and a distinct low energy phenomenology that allows to differentiate it from other models of supersymmetry breaking and mediation mechanisms.

Gauging MSSM global symmetries and SUSY breaking in de Sitter vacuum

We elaborate on a recent study of a model of supersymmetry breaking we proposed recently, in the presence of a tunable positive cosmological constant, based on a gauged shift symmetry of a string modulus, external to the Standard Model (SM) sector. Here, we identify this symmetry with a global symmetry of the SM and work out the corresponding phenomenology. A particularly attracting possibility is to use a combination of Baryon and Lepton number that contains the known matter parity and guarantees absence of dimension-four and -five operators that violate B and L.

Oxygen Supplementing, Biocompatible Outer Membranes for Enhanced Performance of Implantable Glucose Sensors

Lack of linearity and sensitivity, oxygen dependence, biofouling and tissue inflammation hinder the development of implantable biosensors for continuous monitoring of glucose. Herein, we report the development of stacked outer membranes based on LBL/PVA hydrogels that improve sensor sensitivity, linearity, oxygen independence and counter biofouling and inflammation. While the inner LBL membrane affords tunable diffusivity, the outer PVA is capable of releasing anti-inflammatory drugs/tissue response modifying agents to counter acute and chronic inflammation, and to induce neo-angiogenesis at the implant site. Sensors were fabricated by immobilizing GOx enzyme on top of 50 μm platinum wires, followed by deposition of stacked LBL/PVA hydrogel membranes. The response of the sensors at 0.7V to various glucose concentrations was studied. Michelis-Menten analysis was performed to quantify sensor performance in terms of linearity and oxygen dependence. The interplay between sensor performance and inward glucose diffusivity was elucidated using (i) various LBL membranes and (ii) various freeze-thaw (FT) cycles of PVA. Incorporation of LBL/PVA stacked membranes resulted in an 8 fold increase in sensor linearity and a 9 fold decrease in oxygen dependence compared to controls. The enhancement in the sensor performance is attributed to (i) the oxygen storing capability of PVA hydrogel due to the formation of hydrophobic domains during its freezing/ thawing employed for its physical crosslinking and (ii) regulation of glucose flux by the inner LBL membrane. Such membranes offer significant advantages over presently available outer membranes in lieu of (i) their ability to control inflammation, (ii) their modulus that closely matches that of subcutaneous human tissue, (iii) non-necessity of reactive chemical crosslinking agents, (iv) tunable sensitivity and (v) supplemental storage of oxygen.

Fabrication process of Mo/Au TES at RT

We report on the fabrication details of TES based on Mo/Au bilayers. The Mo layer is deposited by radio frequency (RF) sputtering and capped with a sputter deposited thin Au protection layer. Afterwards, a second Au layer of suitable (lower) resistivity is deposited ex‐situ by e‐beam evaporation, until completion of the total desired Au thickness. The deposition was performed at room temperature (RT) on LPCVD Si3 N4 membranes. Such a deposition procedure is very reproducible and allow controlling the critical temperature (Tc) and normal electrical resistance (RN ) of the Mo/Au bilayer. The process is optimized to achieve low stress bilayers, thus avoiding the undesirable curvature of the membranes. Bilayers are patterned using photolithographic techniques and wet etching procedures. Mo superconducting paths are used to contact the Mo/Au bilayers, thus ensuring good electrical conductivity and thermal isolation. The entire fabrication process let to stable and reproducible sensors with required and tunable functional properties

Synchrotron X-ray photoabsorption spectroscopy of plasmas

Theoretical X-ray opacities are used in numerous radiative transfer simulations of plasmas at different temperatures and densities, for example astrophysics, fusion, metrology and EUV and X-rays radiation sources. However, there are only a reduced number of laboratories working on the validation of those theoretical results empirically, in particular for high temperature plasmas (mayor que 1eV). One of those limitations comes from the use of broad band EUV- X ray sources to illuminate the plasma which, among other issues, present low reproducibility and repetition rate [1]. Synchrotron radiation facilities are a more appropriate radiation source in that sense, since they provide tunable, reproducible and high resolution photons. Only their ?low? photon intensity for these experiments has prevented researchers to use it for this purpose. However, as new synchrotron facilities improve their photon fluxes, this limitation not longer holds [2]. This work evaluates the experimental requirements to use third generation synchrotron radiation sources for the empirical measurement of opacities of plasmas, proposing a pausible experimental set-up to carry them out. Properties of the laser or discharge generated plasmas to be studied with synchrotron radiation will be discussed in terms of their maximum temperatures, densities and temporal evolution. It will be concluded that there are encouraging reasons to pursue these kind of experiments which will provide with an appropriate benchmark for theoretical opacities

Amplificador de potencia clase F a 1.64 ghz con control de armónicos

This paper presents a high-power high efficiency PA design method using load pull technique. Harmonic impedance control at the virtual drain is accomplished through the use of tunable pre-matching circuits and modeling of package parasitics. A 0.5 µm GaN high electron mobility transistor (HEMT) is characterized using the method, and loadpull measurements are simulated illustrating the impact of varying 2nd and 3rd harmonic termination. These harmonic terminations are added to satisfy conditions for class-F load pull. The method is verified by design and simulation of a 40-W class-F PA prototype at 1.64 GHz with 76% drain efficiency and 10 dB gain (70% PAE).

Adaptive liquid-crystal phase-only passive devices

This PhD work is focused on liquid crystal based tunable phase devices with special emphasis on their design and manufacturing. In the course of the work a number of new manufacturing technologies have been implemented in the UPM clean room facilities, leading to an important improvement in the range of devices being manufactured in the laboratory. Furthermore, a number of novel phase devices have been developed, all of them including novel electrodes, and/or alignment layers. The most important manufacturing progress has been the introduction of reactive ion etching as a tool for achieving high resolution photolithography on indium-tin-oxide (ITO) coated glass and quartz substrates. Another important manufacturing result is the successful elaboration of a binding protocol of anisotropic conduction adhesives. These have been employed in high density interconnections between ITO-glass and flexible printed circuits. Regarding material characterization, the comparative study of nonstoichiometric silicon oxide (SiOx) and silica (SiO2) inorganic alignment layers, as well as the relationship between surface layer deposition, layer morphology and liquid crystal electrooptical response must be highlighted, together with the characterization of the degradation of liquid crystal devices in simulated space mission environment. A wide variety of phase devices have been developed, with special emphasis on beam steerers. One of these was developed within the framework of an ESA project, and consisted of a high density reconfigurable 1D blaze grating, with a spatial separation of the controlling microelectronics and the active, radiation exposed, area. The developed devices confirmed the assumption that liquid crystal devices with such a separation of components, are radiation hard, and can be designed to be both vibration and temperature sturdy. In parallel to the above, an evenly variable analog beam steering device was designed, manufactured and characterized, providing a narrow cone diffraction free beam steering. This steering device is characterized by a very limited number of electrodes necessary for the redirection of a light beam. As few as 4 different voltage levels were needed in order to redirect a light beam. Finally at the Wojskowa Akademia Techniczna (Military University of Technology) in Warsaw, Poland, a wedged analog tunable beam steering device was designed, manufactured and characterized. This beam steerer, like the former one, was designed to resist the harsh conditions both in space and in the context of the shuttle launch. Apart from the beam steering devices, reconfigurable vortices and modal lens devices have been manufactured and characterized. In summary, during this work a large number of liquid crystal devices and liquid crystal device manufacturing technologies have been developed. Besides their relevance in scientific publications and technical achievements, most of these new devices have demonstrated their usefulness in the actual work of the research group where this PhD has been completed. El presente trabajo de Tesis se ha centrado en el diseño, fabricación y caracterización de nuevos dispositivos de fase basados en cristal líquido. Actualmente se están desarrollando dispositivos basados en cristal líquido para aplicaciones diferentes a su uso habitual como displays. Poseen la ventaja de que los dispositivos pueden ser controlados por bajas tensiones y no necesitan elementos mecánicos para su funcionamiento. La fabricación de todos los dispositivos del presente trabajo se ha realizado en la cámara limpia del grupo. La cámara limpia ha sido diseñada por el grupo de investigación, es de dimensiones reducidas pero muy versátil. Está dividida en distintas áreas de trabajo dependiendo del tipo de proceso que se lleva a cabo. La cámara limpia está completamente cubierta de un material libre de polvo. Todas las entradas de suministro de gas y agua están selladas. El aire filtrado es constantemente bombeado dentro de la zona limpia, a fin de crear una sobrepresión evitando así la entrada de aire sin filtrar. Las personas que trabajan en esta zona siempre deben de estar protegidas con un traje especial. Se utilizan trajes especiales que constan de: mono, máscara, guantes de látex, gorro, patucos y gafas de protección UV, cuando sea necesario. Para introducir material dentro de la cámara limpia se debe limpiar con alcohol y paños especiales y posteriormente secarlos con nitrógeno a presión. La fabricación debe seguir estrictamente unos pasos determinados, que pueden cambiar dependiendo de los requerimientos de cada dispositivo. Por ello, la fabricación de dispositivos requiere la formulación de varios protocolos de fabricación. Estos protocolos deben ser estrictamente respetados a fin de obtener repetitividad en los experimentos, lo que lleva siempre asociado un proceso de fabricación fiable. Una célula de cristal líquido está compuesta (de forma general) por dos vidrios ensamblados (sándwich) y colocados a una distancia determinada. Los vidrios se han sometido a una serie de procesos para acondicionar las superficies internas. La célula se llena con cristal líquido. De forma resumida, el proceso de fabricación general es el siguiente: inicialmente, se cortan los vidrios (cuya cara interna es conductora) y se limpian. Después se imprimen las pistas sobre el vidrio formando los píxeles. Estas pistas conductoras provienen del vidrio con la capa conductora de ITO (óxido de indio y estaño). Esto se hace a través de un proceso de fotolitografía con una resina fotosensible, y un desarrollo y ataque posterior del ITO sin protección. Más tarde, las caras internas de los vidrios se acondicionan depositando una capa, que puede ser orgánica o inorgánica (un polímero o un óxido). Esta etapa es crucial para el funcionamiento del dispositivo: induce la orientación de las moléculas de cristal líquido. Una vez que las superficies están acondicionadas, se depositan espaciadores en las mismas: son pequeñas esferas o cilindros de tamaño calibrado (pocos micrómetros) para garantizar un espesor homogéneo del dispositivo. Después en uno de los sustratos se deposita un adhesivo (gasket). A continuación, los sustratos se ensamblan teniendo en cuenta que el gasket debe dejar una boca libre para que el cristal líquido se introduzca posteriormente dentro de la célula. El llenado de la célula se realiza en una cámara de vacío y después la boca se sella. Por último, la conexión de los cables a la célula y el montaje de los polarizadores se realizan fuera de la sala limpia (Figura 1). Dependiendo de la aplicación, el cristal líquido empleado y los demás componentes de la célula tendrán unas características particulares. Para el diseño de los dispositivos de este trabajo se ha realizado un estudio de superficies inorgánicas de alineamiento del cristal líquido, que será de gran importancia para la preparación de los dispositivos de fase, dependiendo de las condiciones ambientales en las que vayan a trabajar. Los materiales inorgánicos que se han estudiado han sido en este caso SiOx y SiO2. El estudio ha comprendido tanto los factores de preparación influyentes en el alineamiento, el comportamiento del cristal líquido al variar estos factores y un estudio de la morfología de las superficies obtenidas.

Low-density InAs QDs with subcritical coverage obtained by conversion of In nanocrystals

We report growth of InAs/GaAs quantum dots (QDs) by molecular beam epitaxy with low density of 2 μm−2 by conversion of In nanocrystals deposited at low temperatures. The total amount of InAs used is about one monolayer, which is less than the critical thickness for conventional Stranski–Krastanov QDs. We also demonstrate the importance of the starting surface reconstruction for obtaining uniform QDs. The QD emission wavelength is easily tunable upon post-growth annealing with no wetting layer signal visible for short anneals. Microphotoluminescence measurements reveal well separated and sharp emission lines of individual QDs.

High-frequency signal generation using 1550 nm VCSEL subject to two-frequency optical injection

We experimentally investigate high-frequency microwave signal generation using a 1550 nm single-mode VCSEL subject to two-frequency optical injection. We first consider a situation in which the injected signals come from two similar VCSELs. The polarization of the injected light is parallel to that of the injected VCSEL. We obtain that the VCSEL can be locked to one of the injected signals, but the observed microwave signal is originated by beating at the photodetector. In a second situation we consider injected signals that come from two external cavity tunable lasers with a significant increase of the injected power with respect to the VCSEL-by-VCSEL injection case. The polarization of the injected light is orthogonal to that of the free-running slave VCSEL. We show that in this case it is possible to generate a microwave signal inside the VCSEL cavity. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Photonic liquid crystal fiber intermodal interferometer

In this work, we present a novel interferometer based on liquid crystal and photonic crystal fiber technology. The objective of this project is the development of a tunable (switchable) modal (Mach-Zehnder) interferometer for optical communications or sensing. This interferometer has been manufactured splicing a short portion (between 15 and 30 mm) of photonic crystal fiber with two single mode fiber pigtails. The study shows a high sensitivity of the interferometer to the polarization of the launching light.

Nuevas arquitecturas de transpondedores de microondas = New transponder architectures at microwave frequencies = Nouvelles architectures des transpondeurs d’hyperfréquences

En la última década, los sistemas de telecomunicación de alta frecuencia han evolucionado tremendamente. Las bandas de frecuencias, los anchos de banda del usuario, las técnicas de modulación y otras características eléctricas están en constante cambio de acuerdo a la evolución de la tecnología y la aparición de nuevas aplicaciones. Las arquitecturas de los transceptores modernos son diferentes de las tradicionales. Muchas de las funciones convencionalmente realizadas por circuitos analógicos han sido asignadas gradualmente a procesadores digitales de señal, de esta manera, las fronteras entre la banda base y las funcionalidades de RF se difuminan. Además, los transceptores inalámbricos digitales modernos son capaces de soportar protocolos de datos de alta velocidad, por lo que emplean una elevada escala de integración para muchos de los subsistemas que componen las diferentes etapas. Uno de los objetivos de este trabajo de investigación es realizar un estudio de las nuevas configuraciones en el desarrollo de demostradores de radiofrecuencia (un receptor y un transmisor) y transpondedores para fines de comunicaciones y militares, respectivamente. Algunos trabajos se han llevado a cabo en el marco del proyecto TECRAIL, donde se ha implementado un demostrador de la capa física LTE para evaluar la viabilidad del estándar LTE en el entorno ferroviario. En el ámbito militar y asociado al proyecto de calibración de radares (CALRADAR), se ha efectuado una actividad importante en el campo de la calibración de radares balísticos Doppler donde se ha analizado cuidadosamente su precisión y se ha desarrollado la unidad generadora de Doppler de un patrón electrónico para la calibración de estos radares. Dicha unidad Doppler es la responsable de la elevada resolución en frecuencia del generador de “blancos” radar construido. Por otro lado, se ha elaborado un análisis completo de las incertidumbres del sistema para optimizar el proceso de calibración. En una segunda fase se han propuesto soluciones en el desarrollo de dispositivos electro-ópticos para aplicaciones de comunicaciones. Estos dispositivos son considerados, debido a sus ventajas, tecnologías de soporte para futuros dispositivos y subsistemas de RF/microondas. Algunas demandas de radio definida por software podrían cubrirse aplicando nuevos conceptos de circuitos sintonizables mediante parámetros programables de un modo dinámico. También se ha realizado una contribución relacionada con el diseño de filtros paso banda con topología “Hairpin”, los cuales son compactos y se pueden integrar fácilmente en circuitos de microondas en una amplia gama de aplicaciones destinadas a las comunicaciones y a los sistemas militares. Como importante aportación final, se ha presentado una propuesta para ecualizar y mejorar las transmisiones de señales discretas de temporización entre los TRMs y otras unidades de procesamiento, en el satélite de última generación SEOSAR/PAZ. Tras un análisis exhaustivo, se ha obtenido la configuración óptima de los buses de transmisión de datos de alta velocidad basadas en una red de transceptores. ABSTRACT In the last decade, high-frequency telecommunications systems have extremely evolved. Frequency bands, user bandwidths, modulation techniques and other electrical characteristics of these systems are constantly changing following to the evolution of technology and the emergence of new applications. The architectures of modern transceivers are different from the traditional ones. Many of the functions conventionally performed by analog circuitry have gradually been assigned to digital signal processors. In this way, boundaries between baseband and RF functionalities are diffused. The design of modern digital wireless transceivers are capable of supporting high-speed data protocols. Therefore, a high integration scale is required for many of the components in the block chain. One of the goals of this research work is to investigate new configurations in the development of RF demonstrators (a receiver and a transmitter) and transponders for communications and military purposes, respectively. A LTE physical layer demonstrator has been implemented to assess the viability of LTE in railway scenario under the framework of the TECRAIL project. An important activity, related to the CALRADAR project, for the calibration of Doppler radars with extremely high precision has been performed. The contribution is the Doppler unit of the radar target generator developed that reveals a high frequency resolution. In order to assure the accuracy of radar calibration process, a complete analysis of the uncertainty in the above mentioned procedure has been carried out. Another important research topic has been the development of photonic devices that are considered enabling technologies for future RF and microwave devices and subsystems. Some Software Defined Radio demands are addressed by the proposed novel circuit concepts based on photonically tunable elements with dynamically programmable parameters. A small contribution has been made in the field of Hairpin-line bandpass filters. These filters are compact and can also be easily integrated into microwave circuits finding a wide range of applications in communication and military systems. In this research field, the contributions made have been the improvements in the design and the simulations of wideband filters. Finally, an important proposal to balance and enhance transmissions of discrete timing signals between TRMs and other processing units into the state of the art SEOSAR/PAZ Satellite has been carried out obtaining the optimal configuration of the high-speed data transmission buses based on a transceiver network. RÉSUMÉ Les systèmes d'hyperfréquence dédiés aux télécommunications ont beaucoup évolué dans la dernière décennie. Les bandes de fréquences, les bandes passantes par utilisateur, les techniques de modulation et d'autres caractéristiques électriques sont en constant changement en fonction de l'évolution des technologies et l'émergence de nouvelles applications. Les architectures modernes des transcepteurs sont différentes des traditionnelles. Un grand nombre d’opérations normalement effectuées par les circuits analogiques a été progressivement alloué à des processeurs de signaux numériques. Ainsi, les frontières entre la bande de base et la fonctionnalité RF sont floues. Les transcepteurs sans fils numériques modernes sont capables de transférer des données à haute vitesse selon les différents protocoles de communication utilisés. C'est pour cette raison qu’un niveau élevé d'intégration est nécessaire pour un grand nombre de composants qui constitue les différentes étapes des systèmes. L'un des objectifs de cette recherche est d'étudier les nouvelles configurations dans le développement des démonstrateurs RF (récepteur et émetteur) et des transpondeurs à des fins militaire et de communication. Certains travaux ont été réalisés dans le cadre du projet TECRAIL, où un démonstrateur de la couche physique LTE a été mis en place pour évaluer la faisabilité de la norme LTE dans l'environnement ferroviaire. Une contribution importante, liée au projet CALRADAR, est proposée dans le domaine des systèmes d’étalonnage de radar Doppler de haute précision. Cette contribution est le module Doppler de génération d’hyperfréquence intégré dans le système électronique de génération de cibles radar virtuelles que présente une résolution de fréquence très élevée. Une analyse complète de l'incertitude dans l'étalonnage des radars Doppler a été effectuée, afin d'assurer la précision du calibrage. La conception et la mise en oeuvre de quelques dispositifs photoniques sont un autre sujet important du travail de recherche présenté dans cette thèse. De tels dispositifs sont considérés comme étant des technologies habilitantes clés pour les futurs dispositifs et sous-systèmes RF et micro-ondes grâce à leurs avantages. Certaines demandes de radio définies par logiciel pourraient être supportées par nouveaux concepts de circuits basés sur des éléments dynamiquement programmables en utilisant des paramètres ajustables. Une petite contribution a été apportée pour améliorer la conception et les simulations des filtres passe-bande Hairpin à large bande. Ces filtres sont compacts et peuvent également être intégrés dans des circuits à micro-ondes compatibles avec un large éventail d'applications dans les systèmes militaires et de communication. Finalement, une proposition a été effectuée visant à équilibrer et améliorer la transmission des signaux discrets de synchronisation entre les TRMs et d'autres unités de traitement dans le satellite SEOSAR/PAZ de dernière génération et permettant l’obtention de la configuration optimale des bus de transmission de données à grande vitesse basés sur un réseau de transcepteurs.

An autostereoscopic device for mobile applications based on a liquid crystal microlens array and an OLED display

In recent years, many experimental and theoretical research groups worldwide have actively worked on demonstrating the use of liquid crystals (LCs) as adaptive lenses for image generation, waveform shaping, and non-mechanical focusing applications. In particular, important achievements have concerned the development of alternative solutions for 3D vision. This work focuses on the design and evaluation of the electro-optic response of a LC-based 2D/3D autostereoscopic display prototype. A strategy for achieving 2D/3D vision has been implemented with a cylindrical LC lens array placed in front of a display; this array acts as a lenticular sheet with a tunable focal length by electrically controlling the birefringence. The performance of the 2D/3D device was evaluated in terms of the angular luminance, image deflection, crosstalk, and 3D contrast within a simulated environment. These measurements were performed with characterization equipment for autostereoscopic 3D displays (angular resolution of 0.03 ).

A low-cost alternative scheme to detect a 100 Gbps PM-DQPSK signal

We propose and demonstrate a low-cost alternative scheme of direct-detection to detect a 100Gbps polarization-multiplexed differential quadrature phase-shift keying (PM-DQPSK) signal. The proposed scheme is based on a delay line and a polarization rotator; the phase-shift keying signal is first converted into a polarization shift keying signal. Then, this signal is converted into an intensity modulated signal by a polarization beam splitter. Finally, the intensity-modulated signal is detected by balanced photodetectors. In order to demonstrate that our proposed receiver is suitable for using as a PM-DQPSK demodulator, a set of simulations have been performed. In addition to testing the sensitivity, the performance under various impairments, including narrow optical filtering, polarization mode dispersion, chromatic dispersion and polarization sensitivity, is analyzed. The simulation results show that our performance receiver is as good as a conventional receiver based on four delay interferometers. Moreover, in comparison with the typical receiver, fewer components are used in our receiver. Hence, implementation is easier, and total cost is reduced. In addition, our receiver can be easily improved to a bit-rate tunable receiver.

Color uniformity in spotligths - visual perception and system design

La iluminación con diodos emisores de luz (LED) está reemplazando cada vez en mayor medida a las fuentes de luz tradicionales. La iluminación LED ofrece ventajas en eficiencia, consumo de energía, diseño, tamaño y calidad de la luz. Durante más de 50 años, los investigadores han estado trabajando en mejoras LED. Su principal relevancia para la iluminación está aumentando rápidamente. Esta tesis se centra en un campo de aplicación importante, como son los focos. Se utilizan para enfocar la luz en áreas definidas, en objetos sobresalientes en condiciones profesionales. Esta iluminación de alto rendimiento requiere una calidad de luz definida, que incluya temperaturas ajustables de color correlacionadas (CCT), de alto índice de reproducción cromática (CRI), altas eficiencias, y colores vivos y brillantes. En el paquete LED varios chips de diferentes colores (rojo, azul, fósforo convertido) se combinan para cumplir con la distribución de energía espectral con alto CRI. Para colimar la luz en los puntos concretos deseados con un ángulo de emisión determinado, se utilizan blancos sintonizables y diversos colores de luz y ópticas secundarias. La combinación de una fuente LED de varios colores con elementos ópticos puede causar falta de homogeneidad cromática en la distribución espacial y angular de la luz, que debe resolverse en el diseño óptico. Sin embargo, no hay necesidad de uniformidad perfecta en el punto de luz debido al umbral en la percepción visual del ojo humano. Por lo tanto, se requiere una descripción matemática del nivel de uniformidad del color con respecto a la percepción visual. Esta tesis está organizada en siete capítulos. Después de un capítulo inicial que presenta la motivación que ha guiado la investigación de esta tesis, en el capítulo 2 se presentan los fundamentos científicos de la uniformidad del color en luces concentradas, como son: el espacio de color aplicado CIELAB, la percepción visual del color, los fundamentos de diseño de focos respecto a los motores de luz y ópticas no formadoras de imágenes, y los últimos avances en la evaluación de la uniformidad del color en el campo de los focos. El capítulo 3 desarrolla diferentes métodos para la descripción matemática de la distribución espacial del color en un área definida, como son la diferencia de color máxima, la desviación media del color, el gradiente de la distribución espacial de color, así como la suavidad radial y axial. Cada función se refiere a los diferentes factores que influyen en la visión, los cuales necesitan un tratamiento distinto que el de los datos que se tendrán en cuenta, además de funciones de ponderación que pre- y post-procesan los datos simulados o medidos para la reducción del ruido, la luminancia de corte, la aplicación de la ponderación de luminancia, la función de sensibilidad de contraste, y la función de distribución acumulativa. En el capítulo 4, se obtiene la función de mérito Usl para la estimación de la uniformidad del color percibida en focos. Se basó en los resultados de dos conjuntos de experimentos con factor humano realizados para evaluar la percepción visual de los sujetos de los patrones de focos típicos. El primer experimento con factor humano dio lugar al orden de importancia percibida de los focos. El orden de rango percibido se utilizó para correlacionar las descripciones matemáticas de las funciones básicas y la función ponderada sobre la distribución espacial del color, que condujo a la función Usl. El segundo experimento con factor humano probó la percepción de los focos bajo condiciones ambientales diversas, con el objetivo de proporcionar una escala absoluta para Usl, para poder así sustituir la opinión subjetiva personal de los individuos por una función de mérito estandarizada. La validación de la función Usl se presenta en relación con el alcance de la aplicación y condiciones, así como las limitaciones y restricciones que se realizan en el capítulo 5. Se compararon los datos medidos y simulados de varios sistemas ópticos. Se discuten los campos de aplicación , así como validaciones y restricciones de la función. El capítulo 6 presenta el diseño del sistema de focos y su optimización. Una evaluación muestra el análisis de sistemas basados en el reflector y la lente TIR. Los sistemas ópticos simulados se comparan en la uniformidad del color Usl, sensibilidad a las sombras coloreadas, eficiencia e intensidad luminosa máxima. Se ha comprobado que no hay un sistema único que obtenga los mejores resultados en todas las categorías, y que una excelente uniformidad de color se pudo alcanzar por la conjunción de dos sistemas diferentes. Finalmente, el capítulo 7 presenta el resumen de esta tesis y la perspectiva para investigar otros aspectos. ABSTRACT Illumination with light-emitting diodes (LED) is more and more replacing traditional light sources. They provide advantages in efficiency, energy consumption, design, size and light quality. For more than 50 years, researchers have been working on LED improvements. Their main relevance for illumination is rapidly increasing. This thesis is focused on one important field of application which are spotlights. They are used to focus light on defined areas, outstanding objects in professional conditions. This high performance illumination required a defined light quality including tunable correlated color temperatures (CCT), high color rendering index (CRI), high efficiencies and bright, vivid colors. Several differently colored chips (red, blue, phosphor converted) in the LED package are combined to meet spectral power distribution with high CRI, tunable white and several light colors and secondary optics are used to collimate the light into the desired narrow spots with defined angle of emission. The combination of multi-color LED source and optical elements may cause chromatic inhomogeneities in spatial and angular light distribution which needs to solved at the optical design. However, there is no need for perfect uniformity in the spot light due to threshold in visual perception of human eye. Therefore, a mathematical description of color uniformity level with regard to visual perception is required. This thesis is organized seven seven chapters. After an initial one presenting the motivation that has guided the research of this thesis, Chapter 2 introduces the scientific basics of color uniformity in spot lights including: the applied color space CIELAB, the visual color perception, the spotlight design fundamentals with regards to light engines and nonimaging optics, and the state of the art for the evaluation of color uniformity in the far field of spotlights. Chapter 3 develops different methods for mathematical description of spatial color distribution in a defined area, which are the maximum color difference, the average color deviation, the gradient of spatial color distribution as well as the radial and axial smoothness. Each function refers to different visual influencing factors, and they need different handling of data be taken into account, along with weighting functions which pre- and post-process the simulated or measured data for noise reduction, luminance cutoff, the implementation of luminance weighting, contrast sensitivity function, and cumulative distribution function. In chapter 4, the merit function Usl for the estimation of the perceived color uniformity in spotlights is derived. It was based on the results of two sets of human factor experiments performed to evaluate the visual perception of typical spotlight patterns by subjects. The first human factor experiment resulted in the perceived rank order of the spotlights. The perceived rank order was used to correlate the mathematical descriptions of basic functions and weighted function concerning the spatial color distribution, which lead to the Usl function. The second human factor experiment tested the perception of spotlights under varied environmental conditions, with to objective to provide an absolute scale for Usl, so the subjective personal opinion of individuals could be replaced by a standardized merit function. The validation of the Usl function is presented concerning the application range and conditions as well as limitations and restrictions in carried out in chapter 5. Measured and simulated data of various optical several systems were compared. Fields of applications are discussed as well as validations and restrictions of the function. Chapter 6 presents spotlight system design and their optimization. An evaluation shows the analysis of reflector-based and TIR lens systems. The simulated optical systems are compared in color uniformity Usl , sensitivity to colored shadows, efficiency, and peak luminous intensity. It has been found that no single system which performed best in all categories, and that excellent color uniformity could be reached by two different system assemblies. Finally, chapter 7 summarizes the conclusions of the present thesis and an outlook for further investigation topics.

Modal liquid crystal microaxicon array

A novel tunable liquid crystal microaxicon array is proposed and experimentally demonstrated. The proposed structure is capable of generating tunable axicons (thousands of elements) of micrometric size, with simple control (four control voltages) and low voltage, and is totally reconfigurable. Depending on the applied voltages, control over the diameter, as well as the effective wedge angle, can be achieved. Controls over the diameter ranging from 107 to 77 μm have been demonstrated. In addition, a control over the phase profile tunability, from 12π to 24π radians, has been demonstrated. This result modifies the effective cone angle. The diameter tunability, as well the effective cone angle, results in a control over the nondiffractive Bessel beam distance. The RMS wavefront deviation from the ideal axicon is only λ∕3. The proposed device has several advantages over the existing microaxicon arrays, including being simple having a low cost. The device could contribute to developing new applications and to reducing the fabrication costs of current devices.