Incoherent spatial solitons in nematic liquid crystals

Spatial solitons are generated in nematic liquid crystals taking advantage of their reorientational response with increase in refractive index. Such response is saturable and can therefore prevent filamentation even in the fully three-dimensional case. To sustain a soliton, a linearly polarized optical field exerts a torque on the (pre-aligned) induced molecular dipoles of a positive uniaxial liquid crystal, orienting them towards the beam polarization vector. This is obtained at low powers by introducing a pre-tilt to the molecules in a planarly-anchored nematic, as to form an angle close to /spl pi//4 between them and the optical field. Since the liquid crystal has a noninstantaneous response, it averages out rapid intensity variations and allows to employ light with reduced spatio-temporal coherence. When properly polarized, the spatially incoherent beam forms an "incoherent" spatial soliton, which can also guide a weaker copolarized and collinear signal of different wavelength. Coherent/incoherent solitons and their use in signal rerouting and multiplexing are discussed.