SPATIAL OPTICAL SOLITONS GOVERNED BY QUADRATIC NONLINEARITY

We demonstrate that a dielectric medium with purely quadratic nonlinea rity [the so-called chi((2)) material] can display self-focusing pheno mena through a new type of modulational instability of the interacting fundamental and second-harmonic field components and therefore can su pport propagation of (two-wave) optical solitons. We prove the existen ce of a family of such solitons, which are found numerically and, in s ome particular cases, also analytically. The two-wave solitons are sta ble in the whole parameter region in which they exist.