We demonstrate a new sort of optical fibers, which are self-assembled from a smectic-A liquid crystal. When this liquid crystal is put in contact with water solution of surfactant CTAB, microfibers start spontaneously growing at the liquid crystal-water interface. The fibers are of very uniform diameter and can be several hundreds of micrometers long. They all have a line topological defect in the core of the fiber with a local optical axis pointing from the defect core towards the surface. The ends of the fiber are of perfect spherical shape. By doping the fibers with a fluorescent dye, we demonstrate guiding of light along the fiber. When the fiber is illuminated with pulsed light, which is absorbed by the dye, we observe Whispering Gallery Mode (WGM) lasing in a plane perpendicular to the fiber. The smectic-A fibers are soft and flexible and can be manipulated with laser tweezers demonstrating a promising approach for the realization of soft matter photonic circuits.
B.04 Guest lectureCOBISS.SI-ID: 27896359
When liquid crystals are dispersed in an immiscible fluid, microdroplets of liquid crystal are spontaneously formed in a fraction of a second. They have optically anisotropic internal structure, which is determined by the ordering of liquid crystal molecules at the interface. Spherical droplets of a nematic liquid crystal can function as whispering-gallery-mode microresonators with an unprecedented width of wavelength tunability by an electric field. WGM pulsed lasing in dye-doped nematic microdroplets is sensitive to strain, temperature and presence of molecules that change molecular orientation at the interface. Omnidirectional 3D lasing was demonstrated in droplets of chiral nematic liquid crystals that form 3D Bragg-onion resonators. We present recent progress in this field, including electric tuning of 3D lasing from chiral nematic droplets and self-assembly of ferroelectric smectic-C* microdroplets with the onion-Bragg structure. We show that anisotropic fibres could be self-assembled from smectic liquid crystals.
B.04 Guest lectureCOBISS.SI-ID: 27598119
Complex confinement of chiral and achiral nematogenic liquid crystals often leads to stable and metastable disclinations in the orientational order-parameter fields. The constrained mesophases where stabilization of defect-structures is a consequence of a balance between conflicting effects of confining geometries and chirality are a kind of topological liquids. Recently it was shown that nematic braids with knots and links of arbitrary complexity can be realized by the laser manipulation of disclinations entangling colloidal particles in nematic liquid crystals. Introducing the self-linking numbers of discination loops as topological invariants in the conventional topological description of nematic defects enables a classification of knotted nematic disclination networks . The approach will be illustrated with numerically modeled nematic braids that were in part also experimentally identified: i) knotted 2D nematic colloidal crystals, ii) 3D opal structures permeated by nematics, iii) knots in cholesteric droplets, and iv) mutually tangled colloidal knots and defect loops in nematic fields.
B.04 Guest lectureCOBISS.SI-ID: 2712420