NONLINEAR REFRACTION CAUSED BY CASCADED 2ND-ORDER NONLINEARITY IN OPTICAL WAVE-GUIDE STRUCTURES

In crystals that lack a center of inversion, in addition to the third-order nonlinearity a cascaded chi(2):chi(2) second-order nonlinearity contributes to the nonlinear refraction. A coupled-mode theory in the frequency domain is used to investigate theoretically the application of this new nonlinear index of refraction for realizing intensity-dependent temporal and spatial light-field evolution in waveguide structures. The significant modification and the immense enhancement of the effects of purely third-order optical nonlinearity by second-order down-mixing of the driven second-harmonic field with the incoming light at the fundamental are discussed.