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 )

High Efficiency and Wide Color Gamut Liquid Crystal Displays

Liquid crystal display (LCD) has become ubiquitous and indispensable in our daily life. Recently, it faces strong competition from organic light emitting diode (OLED). In order to maintain a strong leader position, LCD camp has an urgent need to enrich the color performance and reduce the power consumption. This dissertation focuses on solving these two emerging and important challenges. In the first part of the dissertation we investigate the quantum dot (QD) technology to improve the both the color gamut and the light efficiency of LCD. QD emits saturated color and grants LCD the capability to reproduce color vivid images. Moreover, the QD emission spectrum can be custom designed to match to transmission band of color filters. To fully take advantage of QD\u27s unique features, we propose a systematic modelling of the LCD backlight and optimize the QD spectrum to simultaneously maximize the color gamut and light efficiency. Moreover, QD enhanced LCD demonstrates several advantages: excellent ambient contrast, negligible color shift and controllable white point. Besides three primary LCD, We also present a spatiotemporal four-primary QD enhanced LCD. The LCD\u27s color is generated partially from time domain and partially from spatial domain. As a result, this LCD mode offers 1.5× increment in spatial resolution, 2× brightness enhancement, slightly larger color gamut and mitigated LC response requirement (~4ms). It can be employed in the commercial TV to meet the challenging Energy star 6 regulation. Besides conventional LCD, we also extend the QD applications to liquid displays and smart lighting devices. The second part of this dissertation focuses on improving the LCD light efficiency. Conventional LCD system has fairly low light efficiency (4%~7%) since polarizers and color filters absorb 50% and 67% of the incoming light respectively. We propose two approaches to reduce the light loss within polarizers and color filters. The first method is a polarization preserving backlight system. It can be combined with linearly polarized light source to boost the LCD efficiency. Moreover, this polarization preserving backlight offers high polarization efficiency (~77.8%), 2.4× on-axis luminance enhancement, and no need for extra optics films. The second approach is a LCD backlight system with simultaneous color/polarization recycling. We design a novel polarizing color filter with high transmittance ( \u3e 90%), low absorption loss (~3.3%), high extinction ratio (\u3e10,000:1) and large angular tolerance (up to ±50˚). This polarizing color filter can be used in LCD system to introduce the color/polarization recycling and accordingly boost LCD efficiency by ~3 times. These two approaches open new gateway for ultra-low power LCDs. In the final session of this dissertation, we demonstrate a low power and color vivid reflective liquid crystal on silicon (LCOS) display with low viscosity liquid crystal mixture. Compared with commercial LC material, the new LC mixture offers ~4X faster response at 20oC and ~8X faster response at -20°C. This fast response LC material enables the field-sequential-color (FSC) driving for power saving. It also leads to several attractive advantages: submillisecond response time at room temperature, vivid color even at -20oC, high brightness, excellent ambient contrast ratio, and suppressed color breakup. With this material improvement, LCOS display can be promising for the emerging wearable display market

Smartphone screens as astrometric calibrators

Geometric optical distortion is a significant contributor to the astrometric error budget in large telescopes using adaptive optics. To increase astrometric precision, optical distortion calibration is necessary. We investigate using smartphone OLED screens as astrometric calibrators. Smartphones are low cost, have stable illumination, and can be quickly reconfigured to probe different spatial frequencies of an optical system's geometric distortion. In this work, we characterize the astrometric accuracy of a Samsung S20 smartphone, with a view towards providing large format, flexible astrometric calibrators for the next generation of astronomical instruments. We find the placement error of the pixels to be 189 nm +/- 15 nm RMS. At this level of error, milliarcsecond astrometric accuracy can be obtained on modern astronomical instruments.Comment: 15 pages, 11 figures; accepted, Journal of Astronomical Instrumentatio

Smartphone Power Consumption Characterization and Dynamic Optimization Techniques for OLED Display

Smartphones have emerged as the most popular and frequently used platform for the consumption of multimedia. Following the rapid growth of application number and the explosion of cellular network bandwidth, high power consumption, and limited battery capacity remain as the major challenges in smartphone designs. Therefore, lots of research is made to characterize and optimize the smartphone power performance. However, the existing research approaches on smartphone power characterization generally ignore the impact from the components' varying performance in different applications, as well as users' behavior during the practical usage. Hence, the power optimization techniques in the modern smartphone are inflexible to adapt to different application scenarios and user behaviors. In this dissertation, I first proposed a new smartphone power consumption characterization and analysis approach -- ``SEER'', which was associated with both user ethological and smartphone evolutionary perspectives. The real-time power consumption is measured with a set of the most popular applications on different generations of Samsung Galaxy smartphones. And deep analysis is made to find how each smartphone component is utilized in different applications, and how the users' daily usage patterns impact on final energy consumption. The experiments show that some traditional power-hungry components, such as Wi-Fi and CPU, actually consume much less energy in practical daily usage. Meanwhile, OLED display panel is still the biggest power consumer in the whole smartphone system; even it's considered the most promising low power display technology. To further optimize the display power consumption with OLED. I further proposed a set of dynamic power optimization techniques for OLED display, balancing the real-time power performance and the user visual perception experience. In this dissertation, the optimization is full-filled at three different levels: 1) Hardware based Optimization: Based on the traditional AMOLED display pixel driver, a novel DVS-friendly OLED driver design is proposed, which can minimize the display color distortion under aggressive supply voltage scaling. Correlated fine-grained DVS schemes (DiViCi) are also proposed to utilize the DVS-friendly driver into video streaming applications. 2) Software based Optimization: Despite the hardware modification, a dynamic OLED power model is built to evaluate the OLED panel power consumption and human visual perception quality assessment. A novel video category based dynamic tone mapping (DaTuM) technique is proposed for video streaming; 3) User Interaction based Optimization: The user interaction and visual perception during the display content capture phase are also taken into consideration, a novel OLED power friendly video recording application (MORPh) was also proposed. Dedicated real-time management and reliability enhancement schemes are explored to promote the applicability of the proposed approaches . Experiments show that, with these power optimization techniques, the OLED display panel power performance on smartphone device is significantly improved with reasonable visual quality controllability

Video enhancement : content classification and model selection

The purpose of video enhancement is to improve the subjective picture quality. The field of video enhancement includes a broad category of research topics, such as removing noise in the video, highlighting some specified features and improving the appearance or visibility of the video content. The common difficulty in this field is how to make images or videos more beautiful, or subjectively better. Traditional approaches involve lots of iterations between subjective assessment experiments and redesigns of algorithm improvements, which are very time consuming. Researchers have attempted to design a video quality metric to replace the subjective assessment, but so far it is not successful. As a way to avoid heuristics in the enhancement algorithm design, least mean square methods have received considerable attention. They can optimize filter coefficients automatically by minimizing the difference between processed videos and desired versions through a training. However, these methods are only optimal on average but not locally. To solve the problem, one can apply the least mean square optimization for individual categories that are classified by local image content. The most interesting example is Kondo’s concept of local content adaptivity for image interpolation, which we found could be generalized into an ideal framework for content adaptive video processing. We identify two parts in the concept, content classification and adaptive processing. By exploring new classifiers for the content classification and new models for the adaptive processing, we have generalized a framework for more enhancement applications. For the part of content classification, new classifiers have been proposed to classify different image degradations such as coding artifacts and focal blur. For the coding artifact, a novel classifier has been proposed based on the combination of local structure and contrast, which does not require coding block grid detection. For the focal blur, we have proposed a novel local blur estimation method based on edges, which does not require edge orientation detection and shows more robust blur estimation. With these classifiers, the proposed framework has been extended to coding artifact robust enhancement and blur dependant enhancement. With the content adaptivity to more image features, the number of content classes can increase significantly. We show that it is possible to reduce the number of classes without sacrificing much performance. For the part of model selection, we have introduced several nonlinear filters to the proposed framework. We have also proposed a new type of nonlinear filter, trained bilateral filter, which combines both advantages of the original bilateral filter and the least mean square optimization. With these nonlinear filters, the proposed framework show better performance than with linear filters. Furthermore, we have shown a proof-of-concept for a trained approach to obtain contrast enhancement by a supervised learning. The transfer curves are optimized based on the classification of global or local image content. It showed that it is possible to obtain the desired effect by learning from other computationally expensive enhancement algorithms or expert-tuned examples through the trained approach. Looking back, the thesis reveals a single versatile framework for video enhancement applications. It widens the application scope by including new content classifiers and new processing models and offers scalabilities with solutions to reduce the number of classes, which can greatly accelerate the algorithm design

COMPRESSIVE IMAGING AND DUAL MOIRE´ LASER INTERFEROMETER AS METROLOGY TOOLS

Metrology is the science of measurement and deals with measuring different physical aspects of objects. In this research the focus has been on two basic problems that metrologists encounter. The first problem is the trade-off between the range of measurement and the corresponding resolution; measurement of physical parameters of a large object or scene accompanies by losing detailed information about small regions of the object. Indeed, instruments and techniques that perform coarse measurements are different from those that make fine measurements. This problem persists in the field of surface metrology, which deals with accurate measurement and detailed analysis of surfaces. For example, laser interferometry is used for fine measurement (in nanometer scale) while to measure the form of in object, which lies in the field of coarse measurement, a different technique like moire technique is used. We introduced a new technique to combine measurement from instruments with better resolution and smaller measurement range with those with coarser resolution and larger measurement range. We first measure the form of the object with coarse measurement techniques and then make some fine measurement for features in regions of interest. The second problem is the measurement conditions that lead to difficulties in measurement. These conditions include low light condition, large range of intensity variation, hyperspectral measurement, etc. Under low light condition there is not enough light for detector to detect light from object, which results in poor measurements. Large range of intensity variation results in a measurement with some saturated regions on the camera as well as some dark regions. We use compressive sampling based imaging systems to address these problems. Single pixel compressive imaging uses a single detector instead of array of detectors and reconstructs a complete image after several measurements. In this research we examined compressive imaging for different applications including low light imaging, high dynamic range imaging and hyperspectral imaging

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