Second-Harmonic Generation of Blue Light in GaN Waveguides

Second-harmonic generation was studied in III-metal-polar GaN films grown on sapphire substrates by metalorganic chemical vapor deposition and formed into ridge waveguides. Broadband near-IR femtosecond pulses of an optical parametric amplifier system were injected by end-fire coupling and the nonlinear response was measured while tuning the central wavelength. A prominent peak was found at 450 nm for 1140 nm thick and 10 μm wide GaN waveguides. The measured second-harmonic peak was in agreement with the modal-dispersion phase matching condition calculated using the dispersion of the extraordinary refractive indices of GaN obtained by prism coupling.