Periodically switched nonlinear structures for frequency conversion: theory and experimental demonstration

In this paper, we report on the analytical study of a first-order quasi-phase-matched structure based on a periodically switched nonlinearity. The general average equations describing parametric wave interaction for this structure are obtained. The theoretical results are then used to analyze the special case of a device based on a semiconductor Al_xGa_1-xAs waveguide for efficient frequency doubling in the mid-infrared to the far-infrared range. The necessary conditions to obtain an optimal configuration are discussed in both continuous wave and femtosecond-pulse regimes. Our analysis indicates that the conversion efficiency obtained should significantly exceed the efficiency obtained with a periodically poled lithium niobate crystal at long wavelengths. Finally, we include the preliminary results of the experimental demonstration of a waveguide device based on alternating domains of GaAs and Al_0.4Ga_0.6As.