Investigation of second-harmonic generation efficiency in a waveguide-side-coupled photonic nanocavity

We theoretically investigate second-harmonic generation (SHG) efficiency in a waveguide-side-coupled photonic nanocavity using coupled-mode-theory-based equations. Using an additional condition for the critical input power, we investigated SHG efficiencies at a very low input power and the critical power. At a very low input power, the SHG efficiency is enhanced by the increase in various Q factors for fundamental and SHG light. Conversely, the maximum SHG efficiency at the critical input power is determined by the Q factors for fundamental light and increases up to 50% in a waveguide-side-coupled photonic nanocavity. Our results provide a design rule for waveguide-side-coupled photonic nanocavities for developing highly efficient SHG devices.