UV second harmonic generation in AlN waveguides with modal phase matching

AlN waveguides on sapphire substrates were fabricated from AlN films grown by metalorganic chemical vapor deposition. By tuning the wavelength of the pump light we demonstrated a second harmonic generation in the UV at 306, 331, and 356 nm using the d33 coefficient and modal dispersion phase matching (MDPM). A theoretical model for MDPM with two- and three-mode interaction in planar waveguides was used to explain the results. Its essential component describes the interaction of two, possibly different, waveguide modes at the fundamental frequency that excite the third mode at doubled frequency. The experimental results were found to agree well with the theoretical model. This work confirmed the application potential of high-quality AlN films as waveguides for nonlinear processes.