A. Piccardi

All-optical steering of soliton waveguides in dye-doped liquid crystals

Soliton induced waveguides can be all-optically readdressed in planar cells by modifying the molecular anchoring with an external light source. Using an elliptically shaped control beam we demonstrate refraction and total internal reflection of spatial solitons in dye-doped nematic liquid crystals.

Nematicon all-optical control in liquid crystal light valves

We discuss the interactions between self-guided light beams and light-induced perturbations in a liquid crystal light valve. The model and data are in perfect agreement.

Spatial solitons in liquid-crystal light valves

Liquid-crystal light valves can control the orientation of a nematic layer under the independent or combined action of applied voltage and impinging light intensity; hence, they offer a unique environment for the propagation of spatial optical solitons or nematicons. We demonstrate nematicon excitation, propagation, and steering in photoconductive light valves.

Interactions of accessible solitons with interfaces in anisotropic media: the case of uniaxial nematic liquid crystals

We investigate, both theoretically and experimentally, spatial soliton interaction with dielectric interfaces in a strongly anisotropic medium with non-locality, such as nematic liquid crystals. We throw light on the role of refractive index gradients as well as optic axis variations in both voltage- and self-driven angular steering of non-local solitons. We specifically address and then employ in experiments a suitably designed electrode geometry in a liquid crystalline cell in order to define and tune a graded dielectric interface by exploiting the electro-optic response of the material through the in-plane reorientation of the optic axis in two distinct regions. We study both refraction and total internal reflection as well as voltage controlled steering of spatial solitons.

Nematicon-enhanced spontaneous symmetry breaking

ABSTRACT We investigate topological and optical spontaneous symmetry breaking in nematic liquid crystals subject to the Fréedericksz transition. Specular nematicon states couple to mirrored distributions of the director due to symmetry breaking, with transverse velocities controlled by beam power in the strong nonlinear regime. Hysteresis in transverse velocity versus incidence angle is observed in the soliton regime.

Nonperturbative Nonlinear Optics in Liquid Crystals

We show that reorientational nematic liquid crystals are an ideal workbench for the investigation of non-perturbative nonlinear optical effects and report light self-steering, power-controlled negative refraction and spontaneous symmetry breaking.

BISTABLE OPTICAL PROPAGATION IN NEMATIC LIQUID CRYSTALS

We demonstrate bistability when beams propagate and self-focus in nematic liquid crystals. Sample configurations subject to the Freedericksz threshold support diffracting as well as self-confined beams for the same input power, leading to hysteresis

Electro-optic routing of spatial solitons in Nematic Liquid Crystals

The great interest arisen in the past decades in optical spatial solitons, i.e. self-confined waves supported by the balance between diffraction and nonlinear self-focusing, stems from their character of light-induced waveguides, thus allowing versatile and reconfigurable schemes for optical signal handling and processing [1]. Nematic Liquid Crystals (NLC) are excellent materials for the generation, propagation and the control of spatial solitons, also known as Nematicons [2]: NLC exhibit large birefringence and transparency, coupled with a high reorientational nonlinearity owing to (mean) molecular rotation induced by quasi-static and/or optical frequency electric fields. In addition, the high nonlocal character of their response stabilizes two-dimensional selfconfinement of beams into solitons [3,4]. Hereby we illustrate planar NLC cell configurations whereby nematicons can be electrically routed by propagating in a non-uniform dielectric with transverse and longitudinal variations of the refractive index and/or the orientation of the optic axis, i.e. by undergoing voltage-driven modulation of linear and nonlinear properties. The numerical models and numerical results are in excellent agreement with the experimental data.

Dark Solitons in Nematic Liquid Crystals

We demonstrate the formation of dark spatial solitons in nematic liquid crystals, with an azo-dye dopant providing the self-defocusing response. A collinear copolarized beam is used to probe the guiding properties of the soliton.

Nematicons in Liquid Crystal Light Valves

Conspicuous efforts have been devoted to exploit spatial solitons for signal processing. In nematic liquid crystals steering of spatial solitons or nematicons has been reported in planar cells. In this Communication, we demonstrate excitation and tunable propagation of spatial solitons in photoconductive Light Valves filled with nematic Liquid Crystals (LCLV). We show that nematicons can be effectively launched and deviated in LCLV, combining self-guidance with parallel nonlinear optical processing.