ALL-OPTICAL SWITCHING IN THE DIRECTIONAL COUPLER CAUSED BY NONLINEAR REFRACTION DUE TO CASCADED 2ND-ORDER NONLINEARITY

The intensity-dependent switching characteristic of the nonlinear coupler is simulated. Here, for the first time, a cascaded chi(2) : chi(2) second-order nonlinearity in addition to the direct chi(3) third-order nonlinearity is used as the switching nonlinearity. The nonlinear refraction due to the cascade process can produce much larger effects than the electronic third-order nonlinearity which yields a reduced switching power of the nonlinear coupler. The description of the dynamics of the switching process suggests that switching of subpicosecond pulses is realizable. The resonance of the cascaded nonlinearity is primarily the resonance of second harmonic generation. Thus, the strength of the cascaded nonlinearity can simply be optimized corresponding to the required bandwidth by adjusting the phase-mismatch.