Double grating design and modeling of second harmonic enhancement by radiation coupling in nonlinear optical waveguides

We analyze in this work the design and the modeling of periodical optical waveguides for second harmonic enhancement in χ(2) nonlinear process. We consider in our analysis the fundamental guided mode (λFU = 1.55 μm) and the second harmonic guided mode (λSH = 0.775 μm) as codirectional modes propagating in a symmetrical waveguide. In particular we analyze the second harmonic coupling efficiency in a GaAs/AlGaAs waveguide by studying the coupling effect of two gratings. The gratings consider the quasi phase matching condition between the fundamental and second harmonic modes, and, the coupling with the radiation modes generated by the diffraction effect. The combined effects of the gratings provide an efficient second harmonic field conversion. The numerical results are obtained through the time domain Hertzian potential modeling. A good agreement between numerical and analytical results is found.