Abstract

In X⁽²⁾ cascading, two relevant phenomena are expected in case of suitable group-velocity mismatch (GVM) and group-velocity dispersion (GVD) material parameters: (i) if the GVM dominates and the low-frequency pulses run with opposite velocities respect to the high-frequency one, then interaction could lead to the so called “non-linear transient pulse compression” or to the elastic scattering of non-trapped soliton pulses, (ii) If the GVD dominates and has the same sign for all three waves, then mutually-trapped dispersion-free bright solitons (or quasi-solitons) are attained, due to the interplay between GVD and nonlinearity. Unfortunately, such operating conditions are hardly achievable in real experiments. Non-linear pulse compression was demonstrated only for very specific crystals and wavelengths; regarding the GVD solitons, they are commonly considered as not obtainable due to the low intrinsic dispersion of available X⁽²⁾ materials, which makes the GVM split the interacting pulses before the trapping mechanism sets in. For a review of the argument, see ref. [1] and references therein.

© 1998 IEEE