Hans Desmet

Modeling nematic liquid crystals in the neighborhood of edges

We present a method to simplify simulation techniques for determining liquid-crystal director orientation in geometries with sharply defined edges and for surfaces with strong anchoring without preferred direction. We show analytically that close to such edges, the liquid crystal can be described by just a few parameters. After examining the solutions, it is explained how these results can avoid the numerical problems that arise when simulating such configurations.

A four-electrode liquid crystal device for 2 pi in-plane director rotation

A novel type of liquid crystal device is described, based on a four-electrode unit, arranged in a hexagonal array. Full three-dimensional simulations were performed using a finite elements algorithm demonstrating a 2 pi rotation of the director in the plane parallel to the substrate surface. Applications for the device are situated in the field of multistable wave plates, spatial light modulators and electrically controllable anchoring.

Wave guiding with liquid crystals

Optical waveguides are widely used in the telecom industry for long distance data transport. Glass fibers are designed to have minimal losses. Different functionalities have been integrated in waveguides, such as wavelength filtering, amplitude modulation and routing. Liquid crystals are promising, because their optical properties can be modified by applying a small voltage or by illumination with light. The variation in optical properties can be exploited in different kinds of waveguide systems. It is possible to generate a wave guide in bulk liquid crystal by modulating the director orientation in an appropriate pattern. Some guided modes in such pure liquid crystals are discussed. Because the liquid crystals are anisotropic, the modes have some unusual properties. The influence of light can lead to director reorientation and modify the waveguiding properties. This optical non-linearity determines largely the light propagation. In hybrid waveguides, liquid crystal are used in combination with a material with higher (in the core) or lower (in the cladding) refractive index. Silicon on insulator waveguides are convenient components to study the tuning possibilities in combination with liquid crystals.