Accurate predictive model for twisted neumatic liquid crystal devicesApplication for generating programmable apodizers and Fresnel lenses

Zusammenfassung

We develop two main subjects in this Ph.D. thesis. In the first subject, weconcentrate on the study of the twisted nematic liquid crystal devices.These are the devices used as displays in the electronics industry. Our goalis to calculate and predict with a high degree of accuracy the complexamplitude transmittance provided by these devices, in order to be used asspatial light modulators in optical processing, diffractive optics, adaptiveoptics, in which phase-only or amplitude-only modulations are required.We have proposed a simplified model to describe the performance of thedevices based on a reverse-engineering procedure. We consider the devicedivided in three regions: two side layers or edges, and a central region,whose widths vary with the applied voltage. By means of this model we areable to predict with a high degree of accuracy the complex amplitudemodulation provided by the device. This prediction capability enables toprogram digital searchs for phase-only or amplitude-only configurations.The results achieved are close to the ideal modulations. We have to useshort wavelengths and configurations with polarizers and wave plates.In the second subject, we use the liquid crystal devices to generatediffractive optical elements for image formation systems. On one hand, wehave produced apodizers, which allow to change the impulse response ofthe optical system (focusing depth, resolution). We have successfullyverified the generation of apodizers using the liquid crystal devices in theamplitude-only regime: these programmable apodizers can be dynamicallychanged and they have the flexibility provided by the control by means of acomputer. On the other hand, we have combined an apodizer and a lens in a single diffractive optical element using the liquid crystal device in thephase-only mode. This new element, the focusing programmable apodizer,allow to modify the impulse response and the focal length dynamically andsimultaneously. In order to generate this new element, we have proposed anew technique to codify complex amplitude information on a quadraticphase-only function. Moreover, we take into account different phenomenadue to pixelated structure of the liquid crystal device, such as the inherentapodizing effect.