Routing Light with Spatial Solitons: Light Localization and Steering in Liquid Crystals – Antonio DeLuca

Date: Mon. February 4th, 2013, 12:30 pm-1:30 pm
Location: Rockefeller 221

Nematic Liquid Crystals (NLCs) support strong nonlinear effects, most of them due to the high birefringence and non-local response. Light self-confinement via reorientational nonlinearity and nonlocality, yields to the creation of robust light filaments named ‘optical spatial solitons’, which can trap, switch and route optical signals. In the last ten years, the attention to NLC systems, due to their large and polarization dependent nonlinearity, allowed the observation of self-focusing and spatial solitons with a significant attention devoted to reduce thermal contributions to the nonlinear phenomena and lower the required optical power. In all the observed cases, self-confinement was observed over short distances (hundreds of micrometers) and with non-negligible thermo-optic effects. Some years ago, a new approach has been proposed for the observation of spatial solitons in planar cells of non doped NLCs, by applying an external electric field which eliminates the threshold inherent to the optical Freedericksz transition and by defining an input interface to control both the molecular orientation and the field polarization. Diffractionless propagation of an laser beam over millimeter distances with milliwatt powers, as well as the all-optical formation of a refractive index channel guiding a weaker laser probe beam will be presented, as well as theoretical and experimental results on spatial soliton formation with either a coherent and incoherent pump beam. All-optical switching/logic can be performed on a signal launched in the soliton-induced waveguides. Through the collisional behavior of solitons in a nonlocal medium, the signal can be steered in angle and output position. A power-dependent X junction, AND, and NOR gates will be presented. A description of a particular tilted cell configuration, with the bulk director orientation at a 45deg angle with respect to the e.m. impinging wave vector, represents the key factor for the observation and characterization, over more than 3 millimeters, of both the extraordinary and ordinary waves propagation, with the possibility to create the first polarization independent spatial soliton. The possibility, then, to steer this soliton by applying an external electric field, over an angle greater than 7deg, is considered the last, but not least, important result in the soliton characterization.