Second-harmonic generation using subwavelength gratings in planar waveguides

We present the first demonstration of second-harmonic generation in integrated optical waveguides using subwavelength corrugated gratings. The gratings are covered with a polymer layer with large second-order nonlinearities. These subwavelength gratings lead to the possibility of realizing backward quasi-phase-matching, where the modes at pump and second-harmonic frequencies propagate in opposite directions. In addition, we demonstrate wavelength-selective distributed out-coupling, leading to a measured conversion efficiency of eta = 5.83 x 10(-6) W-1 with a device length of L = 1 mm.