Resumen de Adaptive micro-optical phase modulators based on liquid crystal technology
This 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.
