Research & Facilities
Studying ordered fluids, their important role in nature and their technical applications is a highly topical subject of research. Together with chemical industry, we investigate electro-optic switching effects in novel liquid crystalline materials for next-generation flat panel displays. In addition, our current research is focused on micro- and nanostructures. Their possible use for generating and detecting light (optoelectronics) or processing and transmitting optical signals (photonics) promises a large potential for future applications. In the graduate program „Micro- und Nanostructures in Optoelectronics and Photonics“ at the University of Paderborn, we develop together with physicists and electrical engineers switchable light sources based on microresonators, prepare and characterize tunable optical fibers for optical information technology and develop ultrathin layers of organic semiconductors for light emitting diodes and photovoltaic effects. Additionally, by dispersing very small amounts of nanoparticles in a liquid crystal, the electro-optic switching performance can be improved and also artificial materials with extremely unusual optical properties (metamaterials) can be fabricated, which become tunable owing to the unique liquid crystal behavior.
Tunable micro- and nanostructures
Photonic crystal fibers contain an array of holes extending along the fiber axis and are exceptionally versatile. They can guide optical signals very efficiently, like conventional light guiding fibers applied in information technology. Infiltration with a LC can turn micro-structured fibers into controllable, integrated color-, intensity- or polarization filters. Metal nanostructures of sub-wavelength size can even yield effective material parameters that are not found in nature. Tunable metamaterials are obtained if plasmonic structures of this kind are embedded in a LC. Their transmission spectra can be controlled by thermal addressing, by applying voltages or by non-linear optical effects, such as the “colossal optical nonlinearity”, an extremely large optical Kerr effect.
Organic light sources
Many optical applications require small and highly efficient optical light sources. Cholesteric LCs show an intrinsic periodic helical structure, which can replace a laser resonator. Dr. Jürgen Schmidtke works very successfully on fabricating and characterizing tunable lasers based on polymer and low molar mass cholesteric LCs. Other classes of LCs, smectic and columnar liquid crystals, can act as organic semiconductors with an unusually high charge carrier mobility. Their electroluminescent application requires sophisticated nanostructures composed ultrathin multilayers. Unlike luminescent polymers, LCs are capable of emitting polarized light. Their performance can be enhanced by embedding in a microresonator.
Electro-optics of ploymer composites and nanoparticle dispersions
Combining the anisotropic optical properties of liquid crystals (LCs) with the mechanical properties of polymers has a large potential for possible applications. Flexible displays, optical polarizing or compensating filters, switchable holograms and optical storage are just a few examples of emerging technologies. Currently, we are working on polymer-stabilized blue phases, which are promising materials for a new generation of liquid crystal displays (LCDs). They exhibit fast switching, high contrast and easy fabrication. The benefits of the underlying optical Kerr effect have been known for a long time, but only the combination with a polymer network enabled enhancing the temperature range of the appearance of LC blue phases to values that are technically needed.
