Quadratic solitons: existence versus excitation

Whole families of stable optical solitons are known to exist in media with quadratic nonlinearity, and evidence of such existence has been demonstrated experimentally during the last years in several materials. However, soliton existence does not always guarantee soliton excitation. On the contrary, suitable conditions must be employed in each particular setting for solitons to be efficiently, or even actually, generated. We overview the recent developments along this line, and illustrate their paramount practical importance by discussing in detail the differences encountered with identical soliton families when they are to be excited in up-conversion or down-conversion processes. Limitations of both, the ideal theoretical predictions and the accessible experimental data are highlighted.