Quasi-Phase-Matching Method Based on Coupling Compensation for Second Harmonic Generation in GaN Waveguides

We report a novel quasi-phase-matching method based on coupling compensation for second harmonic generation in GaN/AlGaN waveguides on sapphire substrates. The proposed method can overcome limitations of periodically oriented GaN waveguides because of spatial periodic modulation of the light intensity along the propagation direction, rather than the conventional spatial periodic modulation of the nonlinear optical coefficients of GaN. The method can be realized by using a dual-planar or dual-ridge waveguide frequency doubler structure. This concept has the potential to open a new range of applications for broadband on-chip nonlinear frequency conversion.