Band-edge and cavity second harmonic conversion in doubly resonant microcavity

Optical second harmonic generation in a doubly resonant amorphous silicon nitride microcavity is investigated in both transmission and reflection configurations. Nonlinear conversion efficiency at Fabry - Perot resonant wavelength strongly depends on the angle of incidence due to different spectral overlap of the first- and second-order cavity modes. The maximum efficiency is found for an angle of incidence corresponding to the exact matching of a double resonance condition, as predicted by theory. A significant nonlinear signal is observed in reflection mode at wavelengths corresponding to second-order stop-band edges. Numerical simulations of the transmitted and reflected second harmonic spectra based on a nonlinear transfer matrix method exhibit good agreement with experimental results by assuming surface nonlinear effects at the multilayer interfaces.