Thomas Caspar Kraan

Modeling liquid-crystal gradient-index lenses

The optical properties of one-dimensional gradient-refractive-index lens arrays based on liquid crystals are studied. We find that it is quite possible, using theoretical methods, to predict angular distributions of the light emanating from such arrays when they are illuminated with collimated monochromatic light. We compare four theoretical methods in relation to experiments. The experimental data and the model, based on a combination of eikonal methods and diffraction, are in close correspondence. Features such as maximal beam width and number of extrema in the angular light distribution are discussed and explained theoretically. We also studied dispersion effects, both experimentally and theoretically, with good agreement between the two.

Study of light distribution through liquid crystal (LC) lens arrays

Refractive index gradient formation in liquid crystal cells during the application of an electric field across patterned electrodes was studied. The cells were characterized by measuring the intensity profile of a parallel beam of light passing through the cells. Most of the measurements were performed using transparent electrodes comprising periodic straight-line patterns with a conducting linewidth of 4μm and various pitches in the range of 34–54μm. The intensity profiles through such cells were studied and it was observed that the intensity showed oscillations as a function of angle. Director profiles were calculated in order to estimate the effective refractive index distribution within the cells. Using this input in theoretical models based on wave theory as well as geometrical optics, intensity profiles could be estimated. The limits of each theory were illustrated and it was shown that the oscillations in the intensity profile could be explained by the wave theory. The effects of the orientation of...