Abstract

The mismatched χ⁽²⁾ interaction is often characterized in terms of effective self-focusing (SF) or self- defocusing (SD): SF is mentioned to occur for positive phase mismatch (Δk=2k₁-k₃, at degeneracy) while SD is expected in the opposite case (Δk<0). The χ⁽²⁾ spatial solitons exist both in SF and in SD regime, the common believe being that their threshold is higher in the latter case. Note that the same asymmetry in the threshold vs. Δk profile is said to hold both when solitons are formed in up and in down conversion, this fact being also supported by direct experimental data (see, for example, [1] for the second-harmonic generation and [2] for the down-conversion).

© 2000 IEEE