Nematicons: Spatial Optical Solitons in Nematic Liquid Crystals

Chapter 12: Twisted and Chiral Nematicons

Urszula A. Laudyn and Miroslaw A. Karpierz

Warsaw University of Technology, Warsaw, Poland

12.1 Introduction

The uniqueness of nematicons is connected with the reorientational nonlinearity, by which light can change the initial orientation of liquid crystals. Such orientation, being the result of long-range interactions between molecules, is introduced at the boundaries and can be modified by electric or magnetic fields [1–3]. Solitary waves in nematic liquid crystals (NLCs) were investigated in capillaries [4–6], but the most often used configurations are planar cells with two parallel glass plates. In such cells, NLC can be homogeneously oriented, for example, in the homeotropic texture (where molecules are perpendicular to the glass plates) [7–9] or in the homogenic (planar) texture (where molecules are parallel to the glass plates) [10, 11]. Configurations in which the mean direction of the molecules (molecular director ) varies across the cell thickness, as in planar cells biased by a low-frequency external electric field [12–14], seem to be promising. A nonhomogeneous initial orientation can also be introduced by the boundary conditions, as in hybridly aligned nematics (molecules parallel to one plate and perpendicular to the second plate) or in twisted nematic liquid crystals (TNLC, in which the molecules are parallel to both plates ...