“…Respectively, the first sub-process is responsible for the generation of the SH field, with the most efficient conversion observed at ∆k = 0, while the second sub-process, also called cascading, can be associated with an effective intensity-dependent change of the phase of the fundamental harmonic (∼ d 2 /∆k), which is similar to that of the cubic nonlinearity (DeSalvo, Hagan, Sheik-Bahae, Stegeman, Vanstryland, and Vanherzeele [1992]; Stegeman, Hagan, and Torner [1996]; Assanto, Stegeman, Sheik-Bahae, and Vanstryland [1995]). This latter effect is responsible for the generation of the so-called quadratic solitons, two-wave parametric soliton composed of the mutually coupled fundamental and second-harmonic components (Sukhorukov [1988]; Torner [1998]; Kivshar [1997]; Etrich, Lederer, Malomed, Peschel, and Peschel [2000]; Torruellas, Kivshar, and Stegeman [2001]; Boardman and Sukhorukov [2001]; Buryak, Di Trapani, Skryabin, and Trillo [2002], and references therein).…”