Temporal solitons in quadratic nonlinear media with opposite group-velocity dispersions at the fundamental and second harmonics

Temporal solitons in quadratic nonlinear media with normal second-harmonic dispersion are studied theoretically. The variational approximation and direct simulations reveal the existence of soliton solutions, and their stability region is identified. Stable solutions are found for large and normal values of the second-harmonic dispersion, and in the presence of large group-velocity mismatch between the fundamental- and second-harmonic fields. The solitons (or solitonlike pulses) are found to have tiny nonlocalized tails in the second-harmonic field, for which an analytic exponential estimate is obtained. The estimate and numerical calculations show that, in the parameter region of experimental relevance, the tails are completely negligible. The results open a way to the experimental observation of quadratic solitons with normal second-harmonic dispersion, and have strong implication to the experimental search for multidimensional “light bullets.”.