Nematic liquid crystals for coherent and incoherent spatial solitons

Self confinement as well as spatial solitons have been investigated in various materials including nematic liquid crystals (NLC). In particular, spatial solitons in planar waveguides were demonstrated by Karpierz et al., while solitons in capillaries filled with dye-doped NLC were reported by Warenghem et al. Recently, using a planar geometry which prevented the undesired de-polarization of the input lift and a voltage-controlled pre-tilt to avoid the occurrence of the Freedericks threshold on the required intensity, we demonstrated three-dimensional spatial solitons in undoped NLC. The solitons are obtained by balancing the beam diffraction with the self-focusing effect due to light-induced reorientation thru dipole-field interaction in a positive uniaxial NLC. By pre-orienting the NLC molecules at angles close to n/4 with respect to the sfield vector, the nonlinear response is maximized and powers as low as a few mW suffice to self-confine a linearly polarized light beam over mm distances. Moreover, due to the inherent saturable character of the reorientation, such solitons are stable and robust unlike their counterparts in ideal Kerr media.