Spatial solitons in nematic liquid crystals

Nematic liquid crystal is an excellent medium for nonlinear optics with nonlinear phenomena arising from molecular reorientation or/and thermal effects. Nematic liquid crystals are also very interesting media for optical spatial solitons creation. Experimental results demonstrated that light beams of only milliwats could be self-trapped at distances of a few millimeters. Such solitons, called nematicons, seems to be promising in applications to all optical switching and routing of signals. In this communication, the main idea leading to create optical solitons due to the reorientational nonlinearity in liquid crystals is presented. Usually the planar or homeotropic texture in layer structures were used. In this paper we report also results obtained in twisted nematics. Light beam propagating in such medium diffracts and due to the structural anisotropy propagates at some angle to the direction of the input light. Both theoretical and recently obtained experimental results are presented.