Nematicons: Spatial Optical Solitons in Nematic Liquid Crystals

Chapter 5: External Control of Nematicon Paths

Armando Piccardi, Alessandro Alberucci and Gaetano Assanto

Nonlinear Optics and OptoElectronics Lab, University ROMA TRE, Rome, Italy

5.1 Introduction

The excitation of spatial solitons in nematic liquid crystals (NLC) relies on dipolar interactions between the elongated organic molecules and the electric field associated to propagating light beams [1, 2]. The NLC reorientational response to low and/or high frequency fields, together with other light-NLC interactions—for instance dye-mediated responses [3, 4]—can also be employed to spatially modulate the distribution of the molecular director. This makes NLC cells one of the most versatile environments to generate largely tunable refractive index profiles. In this chapter, we describe how nematicons propagate within inhomogeneous refractive index distributions and illustrate a few methods to modify their trajectories with the use of external fields.

Whatever is the nature of the director distortion, for example optical or electrical [5], a number of considerations hold valid in all cases. First of all, the NLC dielectric anisotropy affects the interaction, in both quantitative and qualitative ways, with respect to isotropic media: as beam energy travels in general forming a nonzero angle (called walk-off) with respect to the wave-vector [6], a beam can be steered by spatial changes in optic axis, even without altering the phase fronts. Thus, the beam trajectory can depend on walk-off ...