Optical solitary waves escaping a wide trapping potential in nematic liquid crystals: Modulation theory

A nonlinear extension of geometric optics is used to derive a modulation theory solution for the trajectory of an optical solitary wave in a nematic liquid crystal-i.e., a nematicon-in which a wide waveguide has been defined by an externally applied static electric field. This solution is used to find the power threshold for the solitary wave to escape the trapping waveguide. This threshold is found to be in excellent agreement with experimental results.