The self-focusing and the formation of spatial solitons attracted a great deal of attention since the early days of nonlinear optics [1]. Essentially a high-power beam changes the refractive index, writing a waveguide capable to confine the beam itself. Accordingly, spatial solitons behave like optical waveguides for beams at different wavelength and low power [2], thus enabling the generation of integrated optical devices written by the light itself. Several all-optical devices have been demonstrated based on this principle, with particular attention devoted in the last two decades to nematic liquid crystals (NLCs) due to their huge nonlinear response [2]. The main nonlinear mechanism in NLC for CW excitations is reorientational, that is, the extraordinary (e-) wave rotates the optical axis of the material, providing a focusing effect [2]. Nonetheless, NLCs are also subject to a strong thermo-optical effect, typically yielding a defocusing effect for the e-wave [3]. Here we demonstrate the excitation of couples of solitons with a single-humped beam caused by the interaction between reorientational and thermal nonlinearity.
