Thermo-nematicon: an unnatural coexistence of solitons in liquid crystals?

Spatial solitons can be excited in liquid crystal, with the required self-focusing being achieved by setting either a thermal gradient or an orientational one. Although the thermal gradient yields to ordinary wave self-focusing, it also yields to extraordinary wave defocusing, thereby killing the reorientational focusing effect. Thus, coexistence of both solitons looks unlikely. However, by analyzing the optical properties of the used mixture, it is shown that the focusing orientational contribution to the index gradient is two orders of magnitude larger than the thermal defocusing one. Then, by properly choosing the materials and geometry, it becomes possible to excite simultaneously the thermal soliton and the nematicon. This can be done in a large range of optical axis tilt angle. (C) 2008 Optical Society of America