Dr. Francesca Serra: Liquid crystal flower microlenses

Liquid crystal flower microlenses 

Dr. Francesca Serra, University of Pennsylvania, Philadelphia, USA

 

While many efforts are still put in removing topological defects from liquid crystals for their application in displays, the same topological defects can be considered a feature in many other contexts, such as colloidal assembly, biosensing applications, bistable displays and other optical devices

 

Among the various types of defects, focal conic domains (FCDs) in smectic A liquid crystals have a very rich internal structure, which makes them act as gradient refractive index microlenses. When the FCDs assemble on a curved interface, they form a highly ordered structure which was named the "flower structure" because of the radial distribution of the FCDs, its "petals". However, as each FCD is also a microlens, the structure bears an analogy to the compound eyes of insects. The hierarchical size distribution of the microlenses on the curved interface leads to a distribution of focal lengths, decreasing from the center to the periphery of the flower. The system is also sensitive to the polarization of light in analogy to real insect eyes.

In our work, the curved interface is created by spreading a layer of smectic liquid crystal on an array of cylindrical micro-pillars. A flower structure forms around each micro-pillar; its curvature, size and optical properties can be tuned by controlling the volume of smectic liquid crystal, the anchoring conditions and the shape of the micro-pillar.